Flexible heating cover assembly for thermal cycling of samples of biological material

ABSTRACT

A flexible heating cover assembly for an apparatus for heating samples of biological material with substantial temperature uniformity includes a housing having a plurality of engageable enclosure components; a resistive heater having a plurality of heater element areas; a heater backing plate providing stability to the resistive heater; a force distribution system that distributes a force over the heater backing plate; and a support plate providing stiffness for the force distribution system, wherein the arrangement of the resistive heater, the heater backing plate, the force distribution system and the support plate provide substantial temperature uniformity among a plurality of sample tubes for receiving samples of biological material. The flexible heating cover assembly improves the uniformity, efficiency, quality, reliability and controllability of the thermal response during thermal cycling of the biological material.

FIELD OF THE INVENTION

[0001] The present invention relates to a heating cover assembly for anapparatus for heating samples of biological material, and moreparticularly to a flexible heating cover assembly that improves theuniformity, efficiency, quality, reliability and controllability of thethermal response during thermal cycling of DNA samples to accomplish apolymerase chain reaction, a quantitative polymerase chain reaction, areverse transcription-polymerase chain reaction, or other nucleic acidamplification types of experiments.

BACKGROUND OF THE INVENTION

[0002] Techniques for thermal cycling of DNA samples are known in theart. By performing a polymerase chain reaction (PCR), DNA can beamplified. It is desirable to cycle a specially constituted liquidbiological reaction mixture through a specific duration and range oftemperatures in order to successfully amplify the DNA in the liquidreaction mixture. Thermal cycling is the process of melting DNA,annealing short primers to the resulting single strands, and extendingthose primers to make new copies of double stranded DNA. The liquidreaction mixture is repeatedly put through this process of melting athigh temperatures and annealing and extending at lower temperatures.

[0003] In a typical thermal cycling apparatus, a biological reactionmixture including DNA will be provided in a large number of sample wellson a thermal block assembly. It is desirable that the samples of DNAhave temperatures throughout the thermal cycling process that are asuniform as reasonably possible. Even small variations in the temperaturebetween one sample well and another sample well can cause a failure orundesirable outcome of the experiment. For instance, in quantitativePCR, one objective is to perform PCR amplification as precisely aspossible by increasing the amount of DNA that generally doubles on everycycle; otherwise there can be an undesirable degree of disparity betweenthe amount of resultant mixtures in the sample wells. If sufficientlyuniform temperatures are not obtained by the sample wells, the desireddoubling at each cycle may not occur. Although the theoretical doublingof DNA rarely occurs in practice, it is desired that the amplificationoccurs as efficiently as possible.

[0004] In addition, temperature errors can cause the reactions toimproperly occur. For example, if the samples are not controlled to havethe proper annealing temperatures, certain forms of DNA may not extendproperly. This can result in the primers in the mixture annealing to thewrong DNA or not annealing at all. Moreover, by ensuring that allsamples are uniformly heated, the dwell times at any temperature can beshortened, thereby speeding up the total PCR cycle time. By shorteningthis dwell time at certain temperatures, the lifetime and amplificationefficiency of the enzyme are increased. Therefore, undesirabletemperature errors and variations between the sample well temperaturesshould be decreased.

[0005] Prior art heating covers used in PCR heating equipment aresimple, stiff, and relatively inexpensive. The prior art designs havemainly involved a stiff metal plate, a simple resistive heater, and aninsulating cover. Because quantitative data was not generated, theheating covers did not have to control condensation in the biologicalsamples as precisely as the heating covers used in QPCR equipment. Also,because optical data was not collected, the prior art heating coverdesigns were not complicated with the need to provide a means to exciteand collect the optical data through the heating cover. Prior artheating covers used in QPCR heating equipment are mainly derived fromtheir earlier PCR counterparts that provide a means for optical signaltransmission, but, prior art heating covers are still mainly stiffdesigns which do not provide a uniform force distribution about thesample containers.

[0006] Prior art heating covers are difficult to use, expensive,complicated and do not provide uniform thermal contact or uniform forcedistribution about the sample wells. U.S. Pat. No. 5,475,610 disclosesan instrument for performing PCR employing a cover which can be raisedor lowered over a sample block. U.S. Pat. No. 5,475,610 does notdisclose a cover assembly that is flexible to provide a more uniformthermal contact and force distribution on the sample tube caps. U.S.Pat. No. 5,928,907 discloses a system for carrying out real timefluorescence-based measurements of nucleic acid amplification products.U.S. Pat. No. 5,928,907 does not disclose a cover assembly that isflexible to provide a more uniform thermal contact and forcedistribution on the sample tube caps. The prior art does not disclose acover assembly that is flexible to provide a more uniform thermalcontact and force distribution on the sample tube caps.

[0007] In light of the foregoing, there is a need in the art for aflexible heating cover assembly that enhances the thermal responseuniformity, efficiency, quality, reliability and controllability of theDNA sample wells in the thermal cycling apparatus.

SUMMARY OF THE INVENTION

[0008] The present invention is a flexible heating cover assembly thatimproves the uniformity, efficiency, quality, reliability andcontrollability of the thermal response during thermal cycling of DNAsamples to accomplish a polymerase chain reaction, a quantitativepolymerase chain reaction, a reverse transcription-polymerase chainreaction, or other nucleic acid amplification types of experiments.

[0009] The present invention is a flexible heating cover assembly for anapparatus for heating samples of biological material with substantialtemperature uniformity including a housing having a plurality ofengageable enclosure components; a resistive heater located within thehousing, the resistive heater including a plurality of heater elementareas; a heater backing plate engaging the resistive heater andproviding protection and stability to the resistive heater; a forcedistribution system that engages the heater backing plate anddistributes a force over the heater backing plate; and a support plateproviding stiffness for the force distribution system, wherein thearrangement of the resistive heater, the heater backing plate, the forcedistribution system and the support plate provide substantialtemperature uniformity among a plurality of sample tubes for receivingsamples of biological material. The flexible heating cover assemblyimproves the uniformity, efficiency, quality, reliability andcontrollability of the thermal response during thermal cycling of DNAsamples.

[0010] In another aspect of the present invention, the resistive heaterproduces a non-uniform heat distribution along a surface exposed to theplurality of sample tubes. The resistive heater further comprises aplurality of heater element areas including at least one outer heaterelement area and at least one central heater element area.

[0011] In another aspect of the present invention, the heater backingplate is thin to promote flexibility when the heater backing plate isconnected to the resistive heater. The heater backing plate is composedof a thermally conductive material.

[0012] In another aspect of the present invention, the forcedistribution system further comprises at least one spring strip and aspring retainer plate. The at least one spring strip has an elongatedbody and a plurality of spring extensions to distribute the forceuniformly on the heater backing plate.

[0013] In another aspect of the present invention, the support plate hassufficient stiffness to provide a reaction force for the forcedistribution system with minimal deflection of the support plate.

[0014] In another aspect of the present invention, the resistive heater,the heater backing plate, and the support plate each comprise aplurality of aligned sample well openings, each sample well openingcorresponding to a respective sample tube of the plurality of sampletubes.

[0015] The present invention is a flexible heating cover assembly withenhanced functions including the flexibility of the cover assembly andthe force distribution. In addition, the flexible heating cover assemblyof the present invention enables the resistive heater to float in avertical direction, so that the resistive heater has some freedom ofmovement vertically which leads to a more uniform thermal contact andforce distribution and more accurate and consistent results. Theflexible heating cover assembly of the present invention providesthermal insulation for the upper portion of the sample tubes and thesample caps.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in andconstitute a part of this specification, illustrate several embodimentsof the invention and together with the description, serve to explain theprinciples of the invention. The present invention will be furtherexplained with reference to the attached drawings, wherein likestructures are referred to by like numerals throughout the severalviews. The drawings shown are not necessarily to scale, with emphasisinstead generally being placed upon illustrating the principles of thepresent invention.

[0017]FIG. 1 is a top perspective view of a flexible heating coverassembly of the present invention.

[0018]FIG. 2 is a bottom perspective view of a flexible heating coverassembly of the present invention.

[0019]FIG. 3 is a perspective view of a flexible heating cover assemblyof the present invention attached to an apparatus for thermally cyclingsamples of a biological material.

[0020]FIG. 4 is a front sectional view of a flexible heating coverassembly of the present invention attached to an apparatus for thermallycycling samples of a biological material.

[0021]FIG. 5 is a partial enlarged front sectional view of a flexibleheating cover assembly of the present invention.

[0022]FIG. 6 is a top view of a thermal block assembly of a thermalsystem base.

[0023]FIG. 7 is a perspective view of a thermal block assembly of athermal system base.

[0024]FIG. 8 is a perspective sectional view of a sample well of athermal system base.

[0025]FIG. 9 is a perspective view of a sensor cup of a thermal systembase.

[0026]FIG. 10 is a perspective view of a heat sink of a thermal systembase.

[0027]FIG. 11 is a bottom view of a heat sink of a thermal system base.

[0028]FIG. 12 is a top view of a solid state heater a heat sink of athermal system base.

[0029]FIG. 13 is a side view of a solid state heater a heat sink of athermal system base.

[0030]FIG. 14 is a perspective view of a solid state heater of a thermalsystem base.

[0031]FIG. 15 is a top view of a spacer bracket with a solid stateheater of a thermal system base.

[0032]FIG. 16 is a top perspective view of a spacer bracket of a thermalsystem base.

[0033]FIG. 17 is a bottom perspective view of a spacer bracket of athermal system base.

[0034]FIG. 18 is a top view of a heat sink, a bottom resistive heater,and a plurality of solid state heaters of a thermal system base.

[0035]FIG. 19 is a bottom view of a thermal block plate and a pluralityof solid state heaters of a thermal system base.

[0036]FIG. 20 is a top exploded assembly view of a flexible heatingcover assembly of the present invention showing how a stiff supportplate, a spring strip, a spring retainer plate, a heater backing plate,a plurality of heater slides, a resistive heater, a cover assembly skirtinteract with a plurality of biological sample tubes having sample caps.

[0037]FIG. 21 is a bottom exploded assembly view of a flexible heatingcover assembly of the present invention showing how a stiff supportplate, a spring strip, a spring retainer plate, a heater backing plate,a plurality of heater slides, a resistive heater, a cover assembly skirtinteract with a plurality of biological sample tubes having sample caps.

[0038]FIG. 22 is a perspective view of a resistive heater of a flexibleheating cover assembly of the present invention showing a layout of aplurality of heater element areas.

[0039]FIG. 23 is a top perspective view of a resistive heater of aflexible heating cover assembly of the present invention showing athermistor.

[0040]FIG. 24 is a bottom perspective view of a resistive heater of aflexible heating cover assembly of the present invention showing aplurality of insulating pads.

[0041]FIG. 25 is a top view of a resistive heater of a flexible heatingcover assembly of the present invention showing a thermistor.

[0042]FIG. 26 is a side view of a resistive heater of a flexible heatingcover assembly of the present invention.

[0043]FIG. 27 is a perspective view of a heater backing plate of aflexible heating cover assembly of the present invention.

[0044]FIG. 28 is a top view of a heater backing plate of a flexibleheating cover assembly of the present invention.

[0045]FIG. 29 is a top perspective view of a resistive heater engaging aheater backing plate of a flexible heating cover assembly of the presentinvention.

[0046]FIG. 30 is a bottom perspective view of a resistive heaterengaging a heater backing plate of a flexible heating cover assembly ofthe present invention.

[0047]FIG. 31 is a bottom view of a resistive heater engaging a heaterbacking plate of a flexible heating cover assembly of the presentinvention.

[0048]FIG. 32 is a side view of a resistive heater engaging a heaterbacking plate of a flexible heating cover assembly of the presentinvention.

[0049]FIG. 33 is a perspective view of a spring strip of a flexibleheating cover assembly of the present invention.

[0050]FIG. 34 is a top view of a spring strip of a flexible heatingcover assembly of the present invention.

[0051]FIG. 35 is a side view of a spring strip of a flexible heatingcover assembly of the present invention.

[0052]FIG. 36 is a perspective view of a spring retainer plate of aflexible heating cover assembly of the present invention.

[0053]FIG. 37 is a top view of a spring retainer plate of a flexibleheating cover assembly of the present invention.

[0054]FIG. 38 is a top perspective view of a stiff support plate of aflexible heating cover assembly of the present invention.

[0055]FIG. 39 is a bottom perspective view of a stiff support plate of aflexible heating cover assembly of the present invention.

[0056]FIG. 40 is a perspective view of a heater slide of a flexibleheating cover assembly of the present invention.

[0057]FIG. 41 is a front view of a heater slide of a flexible heatingcover assembly of the present invention showing the U-shape of thepreferred heater slide.

[0058] While the above-identified drawings set forth preferredembodiments of the present invention, other embodiments of the presentinvention are also contemplated, as noted in the discussion. Thisdisclosure presents illustrative embodiments of the present invention byway of representation and not limitation. Numerous other modificationsand embodiments can be devised by those skilled in the art which fallwithin the scope and sprit of the principles of the present invention.

DETAILED DESCRIPTION

[0059] A flexible heating cover assembly of the present invention isillustrated generally at 200 in FIGS. 1 and 2. As best shown in FIGS. 20and 21, the flexible heating cover assembly 200 includes a coverassembly skirt 250, a resistive heater 300, a heater backing plate 350,a spring strip 400, a spring retainer plate 450, a stiff support plate500, and a plurality of heater slides 550. The flexible heating coverassembly 200 engages a plurality of biological sample tubes 140 havingsample caps 146.

[0060] As shown in FIG. 3, the flexible heating cover assembly 200 canbe attached to an apparatus for thermally cycling samples of abiological material. The flexible heating cover assembly 200 can beattached to any apparatus for thermal cycling of DNA samples toaccomplish a polymerase chain reaction, a quantitative polymerase chainreaction, a reverse transcription-polymerase chain reaction, or othernucleic acid amplification types of experiments. For example, theflexible heating cover assembly 200 can be attached to the apparatus forthermally cycling samples of a biological material disclosed inassignee's co-pending U.S. patent application Ser. No. 09/364,051, theentirety of which is hereby incorporated by reference. When combinedwith a thermal system base 15 (which contains a thermal block assembly20 for accepting samples and means to heat and cool the thermal blockassembly 20), the flexible heating cover assembly 200 improves thequality of the thermal response of the system for quantitative PCR.

[0061] The thermal system base 15 includes a plurality of sample wellsfor receiving sample tubes of a biological reaction mixture. As shown inFIGS. 3-5, the thermal system base 15 includes a thermal block assembly20. Thermal block assembly 20 includes a flat thermal block plate 22 anda plurality of sample wells 24 for receiving tubes with samples of DNA,as best shown in FIGS. 4, 6 and 7. Thermal block plate 22 issubstantially rectangular and is of sufficient size to accommodate aplurality of sample wells 24 on the top surface, but could be of othershapes (i.e., circular, oval, square). In the embodiment shown in thedrawings, the plate 22 accommodates 96 sample wells 24 in a grid havingeight columns and twelve rows. The sample wells 24 are in an 8 by 12grid with center-to-center spacing between adjacent sample wells 24 ofabout nine millimeters. In other embodiments of the present invention,there may be more or less than 96 sample wells, the sample wellarrangement may vary, and the center-to-center measurement betweenadjacent sample wells 24 may be more or less than nine millimeters. Itis to be understood that the number of sample wells can be varieddepending on the specific application requirements. For example, thesample wells could be arranged to form a grid which is sixteen bytwenty-four, thereby accommodating 384 sample wells. The sample wells 24are conical in shape, as shown in FIG. 8. The walls 25 of the tube areconical, and extend at an angle to the flat plate 22. The bottom 26 ofthe interior of the sample well is rounded. The bottom of each samplewell 24 is attached to the thermal block plate 22. It should beunderstood that the sample wells 24 could have any shape (i.e.,cylindrical, square or similar shapes), so that the inner surface of thesample wells 24 closely mates with the sample tube 140 inserted inside.

[0062] The sample wells 24 are designed so that sample tubes 140 withDNA samples can be placed in the sample wells 24. FIG. 5 shows a partialcut-away cross section with sample tubes 140 placed in the sample wells24. Each sample well 24 is sized to fit the sample tube 140 exterior sothat there will be substantial contact area between the sample tube 140and the interior portion of a sample well wall 25 to enhance the heattransfer to the DNA sample in the sample tube 140 and reduce differencesbetween the DNA mixture and sample well temperatures. The sample tube140 includes a conical wall portion 142 which closely mates with thesample well wall 25.

[0063] The sample tubes 140 are available in three common forms: (1)single tubes; (2) strips of eight tubes which are attached to oneanother; and (3) tube trays with 96 attached sample tubes. The presentinvention is preferably designed to be compatible with any of thesethree designs. The sample tubes 140 may be composed of a plastic,preferably molded polypropylene, however, other suitable materials areacceptable. A typical sample tube 140 has a fluid volume capacity ofapproximately 200 μl, however other sizes and configurations can beenvisaged within the spirit and scope of the present invention. Thefluid volume typically used in an experiment is substantially less thanthe 200 μl sample tube capacity.

[0064] Although the preferred embodiment uses sample wells, other sampleholding structures such as slides, partitions, beads, channels, reactionchambers, vessels, surfaces, or any other suitable device for holding asample can be envisaged. Moreover, although the preferred embodimentuses the sample holding structure for biological reaction mixtures, thesamples to be placed in the sample holding structure are not limited tobiological reaction mixtures. Samples could include any type of productfor which it is desired to heat and/or cool, such as cells, tissues,microorganisms or non-biological product.

[0065] Alternatively, a thin film of clear or opaque material could beattached (to form a seal) to the tops of the sample containers in placeof a series of caps. This type of sample container cover can reduce thelabor associated with cap installation for some users. The flexibleheating cover assembly of the present invention works with this type ofsealed film container cover. Typically, these films are composed of athin plastic with a layer of epoxy which can be cured using heat,pressure, heat and pressure, or UV light.

[0066] As embodied herein and shown for example in FIG. 5, each sampletube 140 also has a corresponding sample tube cap 146 for maintainingthe biological reaction mixture in the sample tube. The caps 146 aretypically inserted inside a top cylindrical surface 144 of the sampletube 140. The caps 146 are relatively clear so that light can betransmitted through the cap 146. The sample tube caps 146 may becomposed of a plastic, preferably molded polypropylene, however, othersuitable materials are acceptable. Each cap 146 has an optical window148 on the top surface of the cap. The optical window 148 in the cap 146is thin, flat, composed of plastic, and allows radiation such asexcitation light to be transmitted to the DNA samples and emittedfluorescent light from the DNA to be transmitted back to an opticaldetection system during cycling.

[0067] A biological probe can be placed in the DNA samples so thatfluorescent light is transmitted in and emitted out as the strandsreplicate during each cycle. A suitable optical detection system candetect the emission of radiation from the sample. The detection systemcan thus measure the amount of DNA which has been produced as a functionof the emitted fluorescent light. Data can be provided from each welland analyzed by a computer.

[0068] As best shown in FIGS. 6 and 7, the thermal block plate 22 isprovided with mounting holes 27. Attachment screws or other fastenerspass through each of the mounting holes 27. The arrangement of thesefasteners will be discussed in greater detail below.

[0069] As best shown in FIGS. 6, 7, and 9, the thermal block assembly 20further includes a plurality of sensor cups 28. The sensor cups 28 arepositioned adjacent the outer periphery of the thermal block plate 22.In the illustrated embodiment, four sensor cups 28 are positionedoutside the grid of sample wells 24. There is at least one sensor cupfor each thermoelectric or solid state heating device used to heat thethermal block assembly 20. The details of the solid state heatingdevices will be discussed below. In the illustrated embodiment, foursolid state heating devices are used, and it is therefore appropriate touse at least four thermal sensors in the sensor cups 28. If more solidstate heating devices were used, then it would be desirable to have moresensor cups 28. Each of the solid state heating devices may heat atslightly different temperatures, therefore the provision of a thermalsensor in a sensor cup 28 for each solid state heater increases thermalblock temperature uniformity.

[0070] The sensor cups 28 each include a thermistor or other suitabletemperature sensor positioned to measure the temperature of the thermalblock plate. Alternate temperature sensors include, but are not limitedto, thermocouples or resistance temperature detectors (RTD). Each typeof temperature sensor has advantages and disadvantages. The temperatureof the thermal block plate 22 at the sensor cup 28 corresponds to thetemperature of adjacent sample wells 24. The temperature data from thesensor cup 28 is sent to a controller which will then adjust the amountof heat provided by the heating devices.

[0071] The thermal block plate 22, the sample wells 24, and the sensorcups 28 are preferably composed of copper alloy with a finish ofelectroplated gold over electroless nickel, although other materialshaving a high thermal conductivity are also suitable. This compositionincreases the thermal conductivity between the components and preventscorrosion of the copper alloy, resulting in faster heating and coolingtransition times. It is important for the thermal block assembly 20 tohave a thermal conductivity chosen to increase the temperatureuniformity of the sample wells 24. Increasing thermal block temperatureuniformity increases the accuracy of the DNA cycling techniques. It isdesirable to obtain substantial thermal block temperature uniformityamong the sample wells 24. For example, in a thermal block assembly 20with 96 sample wells with 200 μl capacity sample wells being used tothermally cycle samples of DNA, it is typically desirable to obtaintemperature uniformity of approximately plus or minus 0.5° C.

[0072] The sample wells 24 and sensor cups 28 are fixed to the topsurface of the thermal block plate 22. Preferably, the sample wells 24and sensor cups 28 are silver brazed to the thermal block plate 22 in aninert atmosphere, although other suitable-methods for fixing the samplewells and sensor cups are known. For example, the design of the thermalsystem base 15 is well suited for a fixing method involving ultrasonicwelding. In this ultrasonic welding method, the sample wells 24 areattached to the thermal block plate 22 using pressure and mechanicalvibration energy. Many copper alloys and other non-ferrous alloys arewell suited for this method. Ultrasonic welding provides the advantagesof excellent repeatability and minimal impact to the original materialproperties because no significant heating is required. Another samplewell fixing method involves a copper casting process. Copper castingwould require design-changes in the geometry of the sample wells 24.Although the casting process would be less expensive than the silverbrazing method, there will be a loss in performance. Therefore, thesilver brazing method described above is the preferred method for fixingthe sample wells 24 to the thermal block plate 22.

[0073] As shown in FIGS. 4 and 10-11, a heat sink 30 transfers heat fromthe thermal block assembly 20 to ambient air located adjacent to theheat sink 30. The heat sink 30 includes a plurality of parallel,rectangular fins 32 extending downward from a base 34. It should beunderstood that the heat sink 30 may be of any well-known type. The heatbase 34 and rectangular fins 32 are preferably made from aluminum,although other suitable materials may be used within the spirit andscope of the invention. The heat sink 30 allows the thermal blockassembly 20 to be quickly and efficiently cooled during thermal cycling.Heat is transferred from the thermal block assembly 20 to the heat sink30 due to the lower temperature of the heat sink 30. The heat whichflows to the heat sink 30 is dissipated from the heat sink rectangularfins 32 to the ambient air which flows between the fins 32.

[0074] The heat sink base 34 includes attachment holes 36 through whichfasteners such as attachment screws pass. The attachment holes 36 extendfrom the top surface 60 to the bottom surface or underside 35 of theheat sink base 34. The details of the attachment means will be describedlater.

[0075] As shown in FIGS. 4, 12-15, and 18-19, at least one solid stateheater 40 supplies heat to the thermal block assembly 20. The solidstate heaters 40 are preferably thermoelectric heaters, such as Peltierheaters, but could also be any other type of heater including, but notlimited to, a resistive heater. The Peltier heaters 40 are preferredbecause they can be controlled to exhibit a temperature gradient.Another advantage of the Peltier heaters 40 is that Peltier heaters 40are capable of providing cooling. The Peltier heaters 40 can becontrolled to cool the thermal block assembly below the ambienttemperature. This cooling is not possible with other types of heaterssuch as a resistive element heater. This cooling allows the Peltierheaters 40 to pump heat from the thermal block assembly to the-heat sink30. The Peltier heaters 40 achieve cooling by changing the electricalcurrent polarity into the Peltier heaters 40. The convective air currentacross the heat sink 30 transfers this heat which has been pumped to theheat sink 30 to the ambient air.

[0076] Each Peltier heater 40 includes two lead wires 41 for supplyingan electrical current through the heater. Each Peltier heater 40 alsoincludes a first side 42 located closer to the thermal block plate 22,and a second side 44 located closer to the heat sink base 34. Duringheating of the Peltier heater 40, the first side 42 will be hot and thesecond side 44 will be cool. During cooling by the Peltier heater 40,the first side 42 will be cool and the second side 44 will be hot. Aspreviously discussed, the hot and cold sides are changed with thereversal of the current flow. A plurality of these heaters are locatedbetween the heat sink 30 and thermal block assembly 20. The number ofPeltier heaters 40 can vary depending on the specific heating andcooling requirements for the particular application. In the illustratedembodiment, four Peltier heaters 40 are provided. The number and shapeof the Peltier heaters 40 can be modified. The system could be alteredsuch that a rectangular Peltier heater 40 could be used, alone or incombination with other rectangular or square Peltier heaters 40. Othershapes of Peltier heaters 40 could also be envisaged. Other types ofPeltier heaters 40, such as two-stage Peltier heaters 40, could also beenvisaged. For example, a two-stage Peltier heater 40 has two levels orstages of heat pumping elements which are separated by a plate. Thesetwo-stage Peltier heaters 40 are typically used in order to create verylarge temperature differences between the cold and hot sides. ThePeltier heaters 40 with more than 2 pumping stages are also possible.

[0077] Each of the Peltier heaters 40 is controlled independently of theother Peltier heaters 40. Independent heater control is desirablebecause each Peltier heater 40 may have slightly different temperaturecharacteristics, that is, if identical currents were placed in each ofthe Peltier heaters 40, each of the Peltier heaters 40 could have aslightly different temperature response. Therefore, by providingtemperature control using multiple sensors and sensor cups for theheaters, each Peltier heater 40 can be separately controlled to enhanceuniform temperature distribution to the thermal block assembly 20.Alternately, the independent temperature control can be used to set up aplurality of temperature zones with different temperatures.

[0078] As shown in FIGS. 4 and 15-17, a spacer, such as a bracket forpositioning the at least one solid state heater. A spacer bracket 46 isprovided above and adjacent to the heat sink base 34. The spacer bracket46 is preferably composed of polyetherimide, although other suitablematerials are also acceptable. A spacer bracket cover 49 is includedabove and adjacent to the spacer bracket 46. The spacer bracket 46includes attachment holes 48 through which fasteners such as theattachment screws pass.

[0079] The spacer bracket 46 includes openings 52 in which the Peltierheaters 40 are positioned. As shown in FIG. 15, for example, two Peltierheaters 40 can be positioned in each of the two openings 52. The leadwires 41 of the Peltier heaters 40 are positioned so that they will bereceived in slots 47 of the spacer bracket. The placement of the leadwires 41 in the slots 47 will prevent significant movement by thePeltier heaters 40 in the bracket, while still allowing slight movement.The slots 47 are dimensioned to be slightly larger than the lead wires41 to allow such slight movement.

[0080] The spacer bracket has bosses 54 around the attachment holes 48which have a thickness such that the thermal block assembly 20 will beplaced in compression. By placing the thermal block assembly 20 incompression, heat transfer can occur more efficiently. For example, byimparting a compressive force, the Peltier heaters 40, the heat sink 30,the thermal block plate 22, and the thermal interface materials will beplaced firmly in contact with one another. It should be understood thatthe spacer bracket 46 can be designed to accommodate a variety ofdifferent Peltier heater 40 configurations. The spacer bracket 46 andthe Peltier heaters 40 are designed so that a minimum amount of heat istransferred to the spacer bracket 46. As shown in FIG. 15, a small gapis provided between the outside edge of the Peltier heaters 40 and theinner surfaces 51 of the inner walls of the openings 52. The gap reducesthe amount of contact between the Peltier heaters 40 and the spacerbracket 46, thereby reducing the amount of heat loss to the spacerbracket 46.

[0081] As shown in FIGS. 4, 10 and 18, a heater is located below thesolid state heaters 40 for heating a bottom portion of the solid stateheaters 40. A plurality of resistive element heaters 58 are provided onthe top surface 60 of the heat sink base 34. It should be understoodthat any other type of suitable heater may also be used. In theillustrated embodiment, resistive element heaters 58 are placed at thefront and back edges of the top surface 60 of the heat sink 30. For thesake of the specification, the front is the portion located adjacent theair exit plate 126 on the right side of in FIG. 3, and the back is theportion located adjacent the opposite air exit plate which cannot beseen in FIG. 3. The positioning of the front and the back resistiveelement heaters helps to provide thermal block temperature uniformity ina manner described in further detail below.

[0082] The Peltier heaters 40 are the primary source used for heatingthe thermal block plate 22. However, the Peltier heaters 40 areprimarily located towards the central portion, in that the Peltierheaters 40 are located in the openings 52 of the spacer bracket 46 asbest shown in FIGS. 15-18. In the absence of the bottom resistiveheater, the Peltier heaters 40 would be directed primarily to thecentral portion of the thermal block plate 22, with the risk ofdecreasing temperatures at the edges of the thermal block plate 22, suchas the front and back portions

[0083] An arrangement for heating the thermal block assembly 20 at thefront and back edges to provide thermal block temperature uniformity isalso used. Resistive heaters 58 are provided for improving thermal blockplate temperature uniformity. The resistive heaters do this by heatingthe edges of the heat sink on which they are attached. This results in adesired temperature gradient in the heat sink 30. The resistive heaters58 do not directly heat the front and back portions of the thermal blockplate 22 through convection or direct contact. The resistive heaters 58also do not contact the Peltier heaters 40. The resistive heaters 58create the temperature gradient in the heat sink 30 by increasing thetemperature of the heat sink 30 at the front and back of the heat sinkbase 34. As a result of the temperature gradient on the heat sink 30,the Peltier heaters 40 transfer a greater amount of heat at the frontand back edges of the Peltier heater 40 which are adjacent to the heatsink 30 at the locations closest to the resistive heaters 58. The hotside of the Peltier heaters 40 will have a hotter temperature at theportion of the Peltier heater 40 closest to the resistive heater.Therefore, the front and back portions of the thermal block plate 22will receive a greater amount of heat transfer than the central portionof the thermal block plate 22. This will ensure that the front and backportions of the thermal block plate 22 which are not adjacent to thePeltier heaters 40 will receive heat transfer by conduction through thethermal block plate 22 and thermal interface elements. It should beunderstood that the number and position of the resistive element heatersis exemplary only and will vary depending on the design requirements.

[0084] As shown in FIGS. 4 and 18, at least one bottom thermal interfaceelement is provided between the bottom of the Peltier heaters 40 and thetop surface of the heat sink 30. The bottom thermal interface elements62 are flat plates positioned between the bottom of the Peltier heaters40 and the top surface 60 of the heat sink 30. A bottom thermalinterface element 62 is provided for each of the openings 52 in thespacer element. Therefore, the two Peltier heaters 40 in the frontopening are provided with a plate of thermal interface material, and thetwo Peltier heaters 40 in the back opening are provided with a secondplate of thermal interface material.

[0085] Each bottom thermal interface element 62 is slightly smaller thanits respective opening 52 in the spacer element. Each bottom thermalinterface element roughly corresponds to the size of the surface area ofthe two Peltier heaters 40 which it covers. For example, as shown inFIG. 18, the bottom thermal interface elements are located immediatelyunderneath the Peltier heaters 40. Only a small portion of the bottomthermal interface element can be shown because the Peltier heaters 40cover the entire surface area of the bottom thermal interface elementsexcept for the portion located in between the two Peltier heaters 40sharing the same opening, as shown in FIG. 18.

[0086] The bottom thermal interface elements 62 have a high rate ofthermal conductivity in order to provide effective heat transfer betweenheat sink 30 and the Peltier heaters 40. In addition, the material isrelatively soft so that the bottom thermal interface elements 62 can becompressed. This allows the Peltier heaters 40 to have a more evenlydistributed surface area with the top of the heat sink 30. An example ofthe type of material to be used in the thermal interface elements is aboron nitride filled silicone rubber. Any other type of suitablematerial is also acceptable.

[0087] As shown in FIGS. 4 and 19, at least one top thermal interfaceelement 64 is provided between the top of the Peltier heaters 40 and thebottom of the thermal block plate 22. A pair of top thermal interfaceelements 64 are located between the top of the Peltier heaters 40 andthe bottom of the thermal block plate 22. During heating by the Peltierheaters 40, the top thermal interface elements conduct the heat from thefirst side 42 of the Peltier heaters 40 to the bottom of the thermalblock plate 22. The top thermal interface elements 64 are similar inshape and size to the bottom thermal interface elements 62, except forthe additional provision of thermal interface wings 65 on the thermalinterface elements. The wings are located on the front and back side ofeach Peltier heater 40. The wings 65 provide heat transfer to the areasof the thermal block plate 22 outside of the Peltier heaters 40. Thewings 65 effectively conduct the additional heat that is generated inthe heat sink 30 and Peltier heaters 40 at the front and back edges dueto the bottom resistive heaters. The wings 65 distribute this heat tothe front and back edges of the thermal block plate 22. This increasesthermal block temperature uniformity. The top thermal interface elements64 are composed of the same material with the relatively high rate ofthermal conductivity as the bottom thermal interface elements 62.

[0088] It should be understood that any number of interface elements,including only one, could be used. The provision of the top and bottomthermal interface elements also allows the Peltier heaters 40 to “float”between the thermal block plate 22 and the heat sink base 34. Thecompressible thermal interface material provides for effective heattransfer among the surfaces while also uniformly loading the Peltierheaters 40 in compression. The use of the compressible thermal interfacematerial increases cycle life and reliability of the Peltier heaters 40.The thermal interface material improves the reliability of the system byaffecting the compressive load imparted onto each Peltier heater 40. Anystructural compressive loading forces are dampened and uniformlydistributed into the Peltier heaters 40 due to the thickness andelastomeric characteristics of the thermal interface material. Due tothe more uniform loads imparted on the Peltier heaters 40, thereliability of the solder joints within each Peltier heater 40 will beimproved. It is important not to overly compress the Peltier heater 40with physical or thermal shock which can result in premature failure.

[0089] The thermal system base 15 further includes a radial fan (notshown) to provide air to the heat sink 30. The radial fan is providedadjacent the bottom fan duct 120. The bottom fan duct 120 has an airinlet opening 122 through which ambient air enters. The circulating airflows upward along the interior of the central fan duct 124. Thecirculating air then enters the spaces between the heat sink rectangularfins 32 and flows along the bottom surface 35 of the heat sink 30. Theheat sink 30 transfers heat to the circulating air which then passes outthrough fan air exit plates 126. The fan air exit plates 126 are boltedonto flanges 128 of the central fan duct 124.

[0090] The thermal system base 15 is designed to increase the cycle lifeand reliability of the Peltier heaters 40. An additional way in whichthe reliability of the Peltier heaters 40 is improved is by matching thethermal coefficient of expansion of the materials used for thestructural components surrounding the Peltier heaters 40. Specifically,the thermal block plate 22, the spacer bracket 46, and the heat sinkbase 34 have all been designed to have very similar thermal coefficientsof expansion. During thermal cycling of a DNA sample, the Peltierheaters 40 are structurally loaded with forces resulting from theexpansion and contraction of these components. By providing similarthermal coefficients of expansion to these materials, the expansion andcontraction forces on the Peltier heaters 40 are minimized, therebyimproving the cycle life of the solder joints within the Peltier heaters40.

[0091] It will be understood that a suitable computer device, such asthat includes a microprocessor, can be incorporated into the controlelectronics. The microprocessor controls the temperature and the amountof time at each temperature in the thermal cycle. The microprocessor canbe programmed to conduct the appropriate thermal cycle for each type ofsample material.

[0092] The means for attaching the various components described abovewill now be described. It is important that the means for attaching thevarious components does not result in significant heat transfer awayfrom the thermal block assembly to the outside of the components. Anyheat transfer which occurs from the thermal block assembly should occurthrough the thermal block plate, thermal interface elements, solid stateheaters and heat sink in order to maximize temperature uniformity. Theseelements are designed to have uniform heating and coolingcharacteristics so that no one area of the thermal block plate will becooled any faster than another area. The attachment fasteners must beprovided in order to attach the thermal block plate 22, the thermalinterface elements, the spacer bracket 46, the solid state heaters 40,and heat sink base 34. The attachment fasteners have been designed tominimize the heat transfer that occurs through the attachment fasteners.

[0093] As best shown in FIGS. 20 and 21, the flexible heating coverassembly 200 of the present invention includes a cover assembly skirt250, a resistive heater 300, a heater backing plate 350, a spring strip400, a spring retainer plate 450, a stiff support plate 500, and aplurality of heater slides 550. The aforementioned components engageeach other to form the flexible heating cover assembly 200. A detaileddiscussion of each of these components will follow.

[0094] The flexible heating cover assembly 200 provides enhancedfunctions including the flexibility of the cover assembly and the forcedistribution. In addition, the flexible heating cover assembly 200enables the resistive heater 300 to float in a vertical direction, sothat the resistive heater 300 has some freedom of movement verticallywhich leads to a more uniform thermal contact and force distribution andmore accurate and consistent results. The flexible heating coverassembly 200 provides thermal insulation for the upper portion of thesample tubes 140 and the sample caps 146.

[0095] The flexible heating cover assembly 200 engages a thermal systembase 15 by a plurality of mechanical interfaces. The mechanicalinterfaces would be present in both the flexible heating cover assembly200 and the thermal system base 15 and enable the functionality of thisflexible heater cover assembly 200 when used in combination with thethermal system base 15. The mechanical interfaces allow a forceconnection to be made between the thermal system base 15 and theflexible heating cover assembly 200 to hold those two systems together.The force of the samples wells (and the reaction of that force in theflexible heating cover assembly 200) needs to imparted into theresistive heater 300 and further transferred into the sample tubes 140and the sample caps 146. The force of the sample tubes 140 can varydepending on the number of sample wells and the contents of the sampletubes 140. The flexible heating cover assembly of the present inventionis designed to provide a force of between about 10 grams to about 30grams, per well, into the sample containers. The force distributionsystem is designed such that only about 10 grams of force, per well, areapplied to low stiffness, low thermal mass sample container formats(i.e., single tubes or strip tubes of 8). For higher stiffness, higherthermal mass sample container formats (i.e., 96 well plates), the forcedistribution system is designed to provide up to about 30 grams offorce, per well. The mechanical interfaces of the flexible heating coverassembly 200 also promote an insulating environment around an upperportion of the sample tubes 140 and the sample caps 146. Thus, themechanical interfaces not only provide a physical barrier between theflexible heating cover assembly 200 and the thermal system base 15, themechanical interfaces also transfer force between the force the flexibleheating cover assembly 200 and the thermal system base 15.

[0096] The mechanical interfaces also allow the flexible heating coverassembly 200 to be located in a preferred position about the thermalsystem base 15 such that a favorable ambient environment is maintainedaround the portion of the sample tubes which extends above the thermalsystem base 15. The mechanical interfaces help control the locationflexible heating cover assembly 200 vertically with respect to thethermal system base 15. Proper vertical positioning of the flexibleheating cover assembly 200 with respect to the thermal system base 15allows for maintenance and support of force imparted by the sample tubes140 and the sample caps 146. If the vertical position of the flexibleheating cover assembly 200 with respect to the thermal system base 15were changed, that force could increase or decrease causing inefficientperformance if the force gets too high or too low.

[0097] It is also important to maintain a favorable ambient environmentaround the portion of the sample tubes 140 which extends above thethermal system base 15. During thermal cycling in quantitative PCR andsimilar procedures, the fluid inside the sample tubes 140 is repeatedlyheated and cooled over a wide temperature range, for example from about50° C. to about 95° C. If the sample tubes caps 146 are not heatedadequately at various times during the thermal cycling, vapor maycondense in the upper walls of the sample tubes 140 and on the insidesurface of the sample tubes caps 146. The vapor and possiblecondensation of the vapor, if it is not a consistent variable in theuser's experiment on a tube-to-tube basis, can affect the fluorescencereadings and impact the performance of the instrument and theconsistency of data. Thus, it is desirable to limit vapor formation. Theresistive heater 300 above the sample tube caps 146 limits the vapor andcondensation formation by maintaining the temperature around the sampletube caps 146 above the dew point temperature to limit the vaporcreation in the air above the liquid sample that can distort thefluorescent readings.

[0098] The benefits of the resistive heater 300 are enhanced if there isa favorable ambient environment in many aspects. First, the ambientenvironment has a temperature closer to the temperature range in theresistive heater 300 (i.e., about 85° C. to about 110° C.). So if thetemperature around the resistive heater 300 is closer to that range, asopposed to the ambient temperature inside the instrument (i.e., about25° C. to about 32° C.), then that elevated ambient temperature is oneaspect that creates a favorable ambient environment. Another aspect ofthe favorable ambient environment is a physical structure around theresistive heater 300 and around the upper portion of the sample tubes140 and the sample tube caps 146 to minimize the free convective airflowand the resulting heat transfer from convection. The airflow can beimpacted by a numerous factors. First, fans external to the flexibleheater cover assembly 200 pull air through the instrument, and the fanscan create moving air inside the instrument. The impact of moving airinside the instrument from the fans should be limited. Also, the impactof the movement of air from moving the entire thermal system in one axisto accomplish the acquisition of the fluorescence data should belimited. As the entire thermal system is moved in one axis to acquirefluorescence data, that movement is also creating higher air movements.The flexible heating cover assembly 200 of the present invention helpsto minimize the convective problems where heat is lost to the ambientenvironment. Thus, the elevated ambient temperature and the lowerconvective coefficient and lower convective heat transfer promote thefunction of the resistive heater 300.

[0099] The thermal system base 15 should have certain characteristics tooptimize the benefits of the flexible heating cover assembly 200 of thepresent invention. First, certain mechanical interfaces of the thermalsystem base 15 help promote or apply the reactive force that is neededto maintain the downward force of the sample tubes 140 so that theflexible heating cover assembly 200 can impart that force into thesample tubes 140 and sample tube caps 146. As discussed above, thethermal system base 15 has a rectangular window frame component that hasa flat surface on at least two of the four perimeter sides. The framecomponent provides vertical position, helps control the ambientenvironment acting as an insulator, and structurally provides a base toclamp the flexible heating cover assembly 200 onto, and provide positionregistration. The thermal system base 15 also has a pivoting clampassembly with four contact points that interface with four points in theflexible heating cover assembly 200. The four contact points arepreferably located near the front corner and the rear corner on a leftside and a right side of the thermal system base 15. The four contactpoints also interface with the pivoting clamping assembly and with theflexible heating cover assembly 200 to create a force connection thattransfers force between the thermal system base 15 and the flexibleheating cover assembly 200. In a preferred embodiment of the presentinvention, the clamp assembly is driven by an electric motor andactivated by a software control. There are also some springs in thatassembly and some mechanical parts that pivot back and forth. The threemain aspects of the mechanical requirements of the thermal system base15 that optimize the benefits of the flexible heating cover assembly 200of the present invention are the preferred position (primarilyvertical), the favorable environment, and then the force application.

[0100] The flexible heating cover assembly 200 of the present inventionis designed to operate with an optical scanning or optical datacollection equipment for quantitative PCR. Numerous features of theflexible heating cover assembly 200 are designed to optimize its usewith optical scanning or optical data collection equipment. First, theplurality of sample well holes in the components of the flexible heatingcover assembly 200 create an optical channel in which the fluorescentdye molecule that is attached to the DNA or that is not attached to theDNA can be excited. The plurality of optical channels provide an opticalavenue for exciting and collecting the optical data. The plurality ofoptical channels also can transmit the emitted fluorescent signal fromthe fluorescent dye in the sample to certain optical components tocollect optical data on the samples. Light travels down the opticalchannels, hits the fluid and any dye surrounding or attached to the DNAin the sample, and the emitted light is bounced back up the opticalchannels and is collected with various optical components. Second,optical data should not only be collected from each sample well, but thesensitivity (or the signal-to-noise performance) is also importantbecause with DNA and the fluorescent molecules that are attached to oraround the DNA, there is a limited amount of physical material and dye.Therefore, the light that is emitted is very minimal, and so sensitivityis important to try to pick up as much of this low-level light aspossible. Therefore, the flexible heating cover assembly 200 is thin toassist with optical sensitivity in the data collection and the opticalperformance. Third, because optical scanning is used to collect thedata, a plurality of stiffening ribs in the stiff support plate 500 inthe flexible heating cover assembly 200 provide stiffness for theflexible heating cover assembly 200. The stiffening ribs are arranged topromote scanning between the stiffening ribs. For example, opticalequipment that scans at a mostly constant velocity can be locatedbetween the stiffening ribs that are in the stiff support plate 500. Ina preferred embodiment of the present invention, the flexible heatingcover assembly 200 operates with an optical scanning or optical datacollection means located above the flexible heating cover assembly 200.In other embodiments of the present invention, optical scanning fromareas other than above the flexible heating cover assembly 200 could beemployed, but there may be cost factors and/or optical complexitieswhich should be considered.

[0101] The flexible heating cover assembly 200 of the present inventionoffers numerous performance advantages over the prior art including, butnot limited to, the following: (1) the distribution of heat in theresistive heater 300; (2) the flexibility of the resistive heater 300;(3) the vertical movement of the resistive heater 300 within theflexible heating cover assembly 200; (4) the stiffness of certaincomponents (i.e., the spring retainer plate 450, the stiff support plate500); and (5) the configuration of the spring strips 400. Otheradvantages of the flexible heating cover assembly 200 of the presentinvention are discussed throughout the specification.

[0102]FIGS. 20 and 21 show the vertical distribution of the variouscomponents of the flexible heating cover assembly 200 as follows fromtop to bottom: (1) the stiff support plate 500; (2) the base of thespring strips 400 on a bottom surface of the spring retainer plate 450;(3) the heater backing plate 350; (4) the resistive heater 300; (5) thecover assembly skirt 250; and (6) the sample caps 146 of the sampletubes 140. Each of the components of the flexible heating cover assembly200 will now be discussed.

[0103] As shown in FIGS. 20 and 21, the cover assembly skirt 250includes a plurality of end caps 260 with a plurality of side supportbars 270. In a preferred embodiment of the present invention, there aretwo end caps 260 and two side support bars 270. In other embodiments ofthe present invention, any number of the end caps 260 and the sidesupport bars 270 may be used. The side support bars 270 engage each ofthe end caps 260 so the combination of end caps 260 and the side supportbars 270 form a perimeter enclosure for the flexible heating coverassembly 200. The various components of the cover assembly skirt 250create a favorable ambient environment due to their shape andcomposition of thermally insulating materials. A shoulder in the stiffsupport plate 500 assists in aligning and fastening the variouscomponents of the cover assembly skirt 250 with an adjacent shoulderthat would allow for some alignment variation. Mechanical fastenersattach the various components of the cover assembly skirt 250. Thoseskilled in the art will recognize that other combinations of mechanicalfasteners are within the spirit and scope of the invention.

[0104] In a preferred embodiment of the present invention, the variouscomponents of the cover assembly skirt 250 are composed of polycarbonate(PC) (common trade names include lexan). Those skilled in the art willrecognize that other materials with similar characteristics could beused within the spirit and scope of the present invention including, butare not limited to, acetal (common trade names include delrin),polyetherimide (PEI) (common trade names include ultem), polyamide(common trade names include zytel and nylon), and similar materials.

[0105] The stiff support plate 500 also contains other mechanicalfeatures which can be used to attach the cover assembly skirt components250 to achieve an ambient environment around the upper portion of thesample tubes 140 and sample tubes caps 146 which is favorable. The stiffsupport plate 500 and various cover assembly skirt components 250minimize the convective heat loss and minimize any convective air flowdisruptions which could degrade the target temperature of the flexibleheater assembly 200 or the thermal system base 15.

[0106] FIGS. 22-26 show varying views of the resistive heater 300 of theflexible heater cover assembly of the present invention. The resistiveheater 300 includes a heater insulation 302, a thermistor 304, and aplurality of heater pads 340. In a preferred embodiment of the presentinvention, the heater insulation 302 is generally rectangular in shapeand has slanted corners 308, a plurality of notched sections 310, aplurality of sample well holes 312. In other embodiments of the presentinvention, other shapes for the heater insulation 302 could be used(i.e., oval, square, and similar shapes) and any number of sample wellholes 312 are present.

[0107] As best shown in FIG. 22, the resistive heater 300 also includesa plurality of outer heater element areas 320 and a plurality of centralheater element areas 330. The resistive heater 300 produces anon-uniform heat distribution along the surface exposed to the sampletubes caps 146 in at least two dimensions (the x dimension and ydimension). In a preferred embodiment of the present invention, theresistive heater 300 generates electrical heat in five primary areasacross the heater insulation 302 including two outer heater elementareas 320 and three central heater element areas 330. One outer heaterelement area 320 is located toward each end of the heater insulation302. In a preferred embodiment of the present invention, the outerheater element area 320 is C-shaped and located along the outer edge ofthe sample well holes 312. The C-shape of the outer heater element area320 provides superior heat balance to achieve an optimized thermaluniformity in the temperature range commonly used for the PCR process(i.e., about 37° C. to about 95° C.). The C-shape of the outer heaterelement area 320 includes a long portion 322 having a tapered portion324 and curved end portions 326. At each end of the heater insulation302, there are eight sample wells along the long portion 322 of theC-shape. The tapered portion 324 is located adjacent rows four and fiveof the eight sample well rows. The tapered portion 324 is thinner thanthe other long portions 322 of the C-shape. The curved end portion 326of the C-shape are wider than the long portion 322 of the C-shape. TheC-shape of the outer heater element area 320 including the taperedportion 324 which provides greater thermal uniformity and a favorablethermal distribution. In other embodiments of the present invention, anynumber of outer heater element areas could be used (i.e., one outerheater element area, three outer heater element areas, four or moreouter heater element areas). In other embodiments of the presentinvention, the outer heater element areas can have many different shapesincluding, but not limited to, columns, spirals, curves, zigzags orsimilar shapes.

[0108] In a preferred embodiment of the present invention, three centralheater element areas 330 are used. The central heater element areas 330have an elongated portion 332 and an end cap section 334 at each end.The end cap section 334 of the central heater element area 330 is widerthan the elongated portion 332 and the end cap section 334 is locatedpast the sample well holes 312 toward the outer edge of the heaterinsulation 302. In a preferred embodiment of the present invention, thecentral heater element areas 330 are column shaped and extend across theheater insulation 302 and are generally parallel to each other. In otherembodiments of the present invention, the central heater element areas330 can have many different shapes including, but not limited to,spirals, curves, zigzags or similar shapes. In other embodiments of thepresent invention, any number of central heater element areas 330 couldbe used (i.e., one central heater element area, two central heaterelement areas, four or more central heater element areas).

[0109] The central heater element areas 330 improve the heating ramprate of the resistive heater 300 from about 0.15° C./sec. to about 0.30°C./sec. The faster response for the resistive heater 300 with thecentral heater element areas 330 allows the resistive heater 300 to becontrolled at a variety of temperatures during the PCR process such thatthe quality of quantitative PCR data is more accurate. During denaturingtemperatures of the PCR process (about 95° C.), the resistive heater 300can be controlled to a higher temperature range (about 100-110° C.).During the annealing or extension temperatures of the PCR process (about37-75° C.), the resistive heater 300 can be controlled to a lowertemperature range (about 55-90° C.). The fast response heatertemperature control for the resistive heater 300 with the central heaterelement areas 330 provides superior thermal uniformity over constanttemperature controlled heater scenarios. The ramp rate of the resistiveheater 300 is sufficient to minimize any condensation which could forminside the sample tube cap surface during thermal cycling.

[0110] The location and distribution of the heating areas in theresistive heater 300 have been optimized to provide improvedquantitative PCR data. The optimized performance is gained when usedwith a thermal system base 15 and an optical scanning configuration asdescribed herein. A heat balance exists between the flexible heatingcover assembly 200 and the thermal system base 15 creates a more uniformtemperature distribution in all sample tubes 140. The heat balance inthe flexible heating cover assembly 200 of the present invention isoptimized for the heat distribution that is present in the heating andcooling aspects of the thermal system base 15 discussed above which ispreferred to be a copper block assembly. The flexible heating coverassembly 200 and the thermal system base 15 balance each other, and if adifferent thermal system base has a different thermal distribution, theperformance of the flexible heating cover assembly 200 may not beoptimized. With a different thermal system base 15 and/or opticalscanning methods, it may be necessary to adjust the hardware or controlsoftware to obtain optimized thermal performance.

[0111] The resistive heater 300 not only has central heater elementareas 330, but other heating element areas to improve the performance ofthe resistive heater 300. The resistive heater 300 contains a pluralityof heat carrier circuits 336 which are not electrically connected to theheater power source, but act to increase the thermal conductivity of theresistive heater 300. The plurality of heat carrier circuits 336 help tooptimize the thermal uniformity for the thermal system base 15. In theresistive heater 300, the presence of the heat carrier circuits 336improves that thermal connectivity across the heater in the X and Ydirections. Placing the plurality of heat carrier circuits 336 that arenot electrically connected in various areas of the heater insulation 302increases the speed of the heat movement through the heater insulation302 in the X and Y directions and improves performance of the entiresystem.

[0112] As shown in FIG. 22, the heat carrier circuits 336 are generallyC-shaped and are located inside the C-shaped outer heater element area320. In a preferred embodiment of the present invention, two heatcarrier circuits 336 are used. One heat carrier circuit 336 is locatedon the left side of the heater insulation 302 and another heat carriercircuit 336 is located on the right side of the heater insulation 302.Each heat carrier circuit 336 includes an elongated portion 337 and aplurality of legs 338. The legs 338 of the heat carrier circuits 336 arelonger than the curved end portions 326 of the C-shaped outer heaterelement area 320. In addition, the heat carrier circuits 336 aregenerally thinner than the C-shaped outer heater element areas 320located adjacent to the heat carrier circuits 336. The heat carriercircuit 336 is preferably composed of a conductive metallic materialalthough those skilled in the art will recognize that the heat carriercircuit 336 can be composed of any conductive material. In otherembodiments of the present invention, any number of heat carriercircuits 336 could be used (i.e., one heat carrier circuit, three heatcarrier circuits, four or more heat carrier circuits).

[0113] In a preferred embodiment of the present invention, both heatcarrier circuit 336 help speed transfer through the heater insulation302. The heat carrier circuit 336 located on the right side of theheater insulation 302 is not connected to either the heater power sourceor any lead wires 344. The heat carrier circuit 336 located on the leftside of the heater insulation 302 is electrically connected to two leadwires which allows the heat carrier circuit 336 located on the left sideof the heater insulation 302 to act as a temperature-sensing devicebecause it is electrically connected to lead wires (but not to theheater power source). As the heater temperature changes, the resistanceof the left side heat carrier circuit 336 changes in a predictablemanner. The resistance of the left side heat carrier circuit 336 can bemonitored through the lead wires 344, and used to provide a controlmeans to the heater power source for heater temperature control.

[0114] The resistive heater 300 also contains the thermistor 304 and athermistor lead circuit 306. The thermistor 304 is an electroniccomponent whose resistance changes with temperature. The voltage andcurrent of the thermistor 304 can be measured as the temperaturechanges. The thermistor 304 is located toward the center portion of theheater insulation 302. The thermistor lead circuit 306 extends from thethermistor 304 and uses a trace routing 307 to connect the thermistor304 to a wire exit area near the plurality of heating pads 340. Thethermistor lead circuit 306 follows a path from the thermistor 304 alongthe outer edge of the heater insulation 302 to the wire exit area wherethe thermistor lead circuit 306 connects to two of the four lead wires344. The thermistor lead circuit 306 has a small profile which isadvantageous because it functions without bulky wires that could disruptthe heater-to-sample tube cap thermal interface and/or the thermaldistribution along the heater insulation 302.

[0115] The location of the thermistor 304 also provides advantages overthe prior art. The response the resistive heater is driven by thelocation of the thermistor 304 on the heater insulation 302. Prior artheater assemblies located the thermistor in the corner of the heaterinsulation near the wire exit area because then the thermistor leadcircuit is short and simple. However, because the heat distribution isgreater near the corners, sides, and, to some extent, the perimeter ofthe heater insulation 302 if the thermistor is located the corner, thecontrol of the resistive heater 300 is driven primarily by the cornertemperature. This can cause a time-lag problem with the control andperformance of the center portion of the heater insulation that has asmaller heat distribution than the corners of the heater insulation. Thetime-lag problem results in the center portion of the heater insulationlagging behind the control of the corner and perimeter portions of artof the heater insulation. The flexible heating cover assembly 200 of thepresent invention eliminates much of the time-lag problem by locatingthe thermistor 304 toward the center portion of the heater insulation302. The location of the thermistor 304 near the center of the resistiveheater 300 provides greater control of the vapor and condensationenvironment. The dew-point temperature is controlled by the targettemperature of the sample block, the ambient temp around the sampletubes 140, the pressure inside the sample tubes 140, and the fluidvolume inside the sample tubes 140. Thus, locating the thermistor 304toward the center portion of the heater insulation 302 improves theperformance of the resistive heater 300.

[0116] The design characteristics and dimensions of the resistive heater300 also promote performance. The heater insulation 302 refers to thematerial surrounding the heater element areas. The heater insulation 302also accounts for almost the entire thickness of a the resistive heater300 because the heater insulation 302 is usually much thicker than theheater element areas. The heater insulation 302 is preferably composedof silicone rubber, which provides insulation for the resistive heater300. The silicone rubber surface is relatively soft to promoteflexibility of the resistive heater 300 allowing the resistive heater300 to contact all the sample tube caps 146 to promote conductive heattransfer. The silicone rubber material also provides a superiormechanical connection with the heater backing plate which will bediscussed below. Other materials that could be used for the heaterinsulation 302 include, but are not limited to, polyimide (P1) (commontrade names include kapton), mica, polyester, nomex, and other similarmaterials. Kapton is a common insulating material that used in variousapplications including flex circuits, flexible heaters and resistiveheaters. Kapton is a very good electrical insulator and a good thermalinsulator. Mica is another insulating material that is used in heatersfor other performance reasons. Those skilled in the art will recognizethat other insulating materials known in the art would be within thespirit and scope of the present invention.

[0117] The resistive heater 300 should be thick enough to generate afavorable temperature gradient to promote optimized thermal uniformitywith the thermal system base 15, yet thin enough to allow rapid heatingand cooling during thermal cycling. The preferred thickness of theheater insulation 302 is 0.026 inches which is relatively thin, althoughthose skilled in the art will recognize that other thicknesses would bewithin the spirit and scope of the present invention. The weight of theresistive heater 300 is kept lower because the heater insulation 302contains the plurality of sample well holes 312 which provide opticaltransmission capability and are sized to permit emitted radiation topass through consistent with an optical scanning from aboveconfiguration.

[0118] As shown in FIG. 22, the resistive heater 300 also includes aplurality of heating pads 340 with a plurality of power source wires 342and a plurality of lead wires 344 extending from the heating pads 340.In a preferred embodiment of the present invention, two heating pads 340are located at each of the rear corners of a bottom side 303 of theheater insulation 302. The heater pads 340 have a larger thermal massand tend to absorb heat which takes away heat that could otherwise betransferred in the heater insulation 302. The heating pads 340 provide aconnection area between the lead wires and the other components of theresistive heater 300.

[0119] The heating pad attached to the left side of the heaterinsulation 302 has two power source wires 342 that are connected to theheater power source so a voltage is carried through the two power sourcewires 342. The power source wires 342 are connected to the heater powersource and extend into the heater pad 340 where they connect throughtrace routings 347 with the outer heater element areas 320 and theplurality of central heater element areas 330. In a preferred embodimentof the present invention, the power source wires 342 connect to theheater power source for and also connect to the C-shaped outer heaterelement area 320 on the left side of the heater insulation 302 which isconnected to the three central heater element areas 330 which isconnected to C-shaped outer heater element area 320 on the right side ofthe heater insulation 302. Thus, two power source wires 342 supplyelectrical power to the two outer heater element areas 320 and the threecentral heater element areas 330 which are connected in one circuit.

[0120] The heating pad 340 attached to the right side of the heaterinsulation 302 has four lead wires 344 that are connected to the heatingpad 340. Two of the lead wires 344 are electrically connected to thethermistor 304 through trace routings 307 and then the other two leadwires 344 are connected to the heat carrier circuit 336 located on theleft side of the heater insulation 302 to increase the speed of heattransfer.

[0121] As shown in FIGS. 27 and 28, the flexible heater cover assemblyalso includes the heater backing plate 350. The heater backing plate 350is thin, flexible, and thermally conductive. The heater backing plate350 is similar in size and shape to the resistive heater 300. Thepreferred thickness of the heater backing plate 350 is 0.018 inches,although those skilled in the art will recognize that other thicknesseswould be within the spirit and scope of the present invention. Theheater backing plate 350 also contains a plurality of sample well holes352, a plurality of narrow slots 354, a plurality of corner slots 356, aplurality of securing holes 358, a plurality guide cut-outs 360, and athermistor cut-out 362.

[0122] The heater backing plate 350 has a plurality of sample well holes352 designed to allow the sample tubes 140 to fit in the sample wellholes 352. In a preferred embodiment of the present invention, there are96 sample wells and 96 corresponding sample well holes 352 in the heaterbacking plate 350. The weight of the heater backing plate 350 is keptlower because the heater backing plate 350 contains the plurality ofsample well holes 352 which provide optical transmission capability andare sized to permit emitted radiation to pass through consistent with anoptical scanning from above configuration. As discussed above, othernumbers of tubes 140 and sample well holes 352 are within the spirit andscope of the present invention.

[0123] As shown in FIG. 28, the plurality of narrow slots 354 throughoutthe heater backing plate 350 promote the flexibility of the plate 350and direct heat transfer on the plate 350. The slots 354 are mainly inthe horizontal X direction between the plurality of sample well holes352. The slots 354 oriented in generally parallel rows between each rowof sample well holes 352. A reasons for this orientation of the slots354 is that the main heat flow in the heater backing plate 350 is in thehorizontal X direction both toward the center, and away from the centertoward the sides. Although there is some heat flow in the vertical Ydirection, the primary heat flow in the heater backing plate 350 is inthe horizontal direction from left to right or right to left. The slots354 are oriented to minimize the retardation of that heat flow in atleast one direction. The slots 354 promote flexibility while notdisrupting the ability of the heat to flow freely in the heater backingplate 350.

[0124] The number and configuration of the slots 354 is designed tofacilitate heat flow in the heater backing plate 350 and to notinterfere with the heat emanating from the central heater element areas330. The slots 354 are arranged in either a single slot or a double slotformation throughout the heater backing plate 350 with the single slots354 located toward the center of the plate 350, and the double slots 354are located toward the outer edges of the plate 350. The single slot 354configuration toward the center of the heater backing plate 350 isarranged so that the central heater element areas 330 do not cross overa slot. Thus, the central heater element areas 330 are completelycovered by the a solid metallic material of the heater backing plate350. If the central heater element areas 330 would cross over the slot354, a local temperature differential would be created. The localtemperature differential creates a thermal stress that decreases thereliability of the resistive heater 300 and could even cause failure ofthe resistive heater 300. The double slots 354 toward the outer edges ofthe heater backing plate 350 promote heat flow in the Y direction andminimize the thermal barrier between sample well holes 352 in the Ydirection. The number and configuration of the slots 354 is designed tominimize the disruption of conductive heat flow through the heaterbacking plate 350.

[0125] Each back corner of the heater backing plate 350 contains aplurality of corner slots 356 that are diagonally oriented to create aheat barrier. When the heater backing plate 350 is attached to theresistive heater 300, the heater pads 340 of the resistive heater 300have a much larger thermal mass than the heater backing plate 350 whichis thin. Thus, heat is drawn toward the corners of the heater backingplate 350 where the heater pads 340 with larger thermal mass arelocated. Further, the heater pads 340 tend to absorb heat which takesaway heat that could otherwise heat the heater backing plate 350. Theplurality of corner slots 356 create a heat barrier that diverts heatthat would otherwise be drawn to the larger thermal mass of the heaterpads 340 to other portions of the heater backing plate 350. Thus, theplurality of corner slots 356 assist in efficiently heating the plate350 and minimize the disruption of conductive heat flow through theheater backing plate 350.

[0126] The heater backing plate 350 also contains the plurality ofsecuring holes 358. A plurality of securing pins are placed in thesecuring holes 358 to insure that the resistive heater 300 and theattached heater backing plate 350 are retained at all times in theflexible heating cover assembly 200 during loading and unloading of thesample tubes 140. In a preferred embodiment of the present invention,four securing holes 358 and securing pins are used. Those skilled in theart will recognize that other number of securing holes 358 and securingpins would be within the spirit and scope of the present invention. Thesecuring holes 358 in the heater backing plate 350 are larger than thepins so that the resistive heater 300 may move vertically about the pinswithout a large friction force. This vertical movement of the resistiveheater 300 can accommodate the range of installed heights for varioussample tubes 140 formats and various tolerances.

[0127] The heater backing plate 350 contains the plurality of guidecut-outs 360 that are used as a guide interface. In a preferredembodiment of the present invention, four guide cut-outs 360 are used.Those skilled in the art will recognize that other number of securingholes 358 and securing pins would be within the spirit and scope of thepresent invention. In addition, the heater backing plate 350 containsthe thermistor cut-out 362 that permits the thermistor 304 to projectthrough the heater backing plate 350 when the plate 350 is attached tothe resistive heater 300. The thermistor cut-out 362 is slightly largerthan the size of the thermistor 304 so not to interfere with temperaturechange readings from the thermistor 304.

[0128] The heater backing plate 350 should be thermally conductive sothat the ramp rate of the resistive heater 300 is not degraded by theadded thermal mass of the heater backing plate 350. Because the heaterbacking plate 350 should be thermally conductive, thin, and flexible,the heater backing plate 350 can be composed of a metallic material. Ina preferred embodiment of the present invention, the heater backingplate 350 is composed of aluminum alloy 1100 with a temper designationof H12 or H14. Other aluminum alloys that could be used within thespirit and scope of the present invention include, but are not limitedto, aluminum 6061-T6, aluminum 6063, aluminum 5032 and similar aluminumalloys. Those skilled in the art will recognize that other aluminumalloys known in the art would be within the spirit and scope of thepresent invention. In addition, any other thermally-conductive metalthat is available a thin foil or a thin plate form could be used withinthe spirit and scope of the present invention. Other thermally-conductedmetals that could be used include, but are not limited to, copperalloys, silver alloys, carbon steel, stainless steel and similar metals.Those skilled in the art will recognize that other metals and alloysknown in the art would be within the spirit and scope of the presentinvention.

[0129] As shown in FIGS. 29-32, the bottom surface of the heater backingplate 350 is connected to the resistive heater 300 to provide protectionand stability while promoting heat transfer. The heater backing plate350 provides protection for the resistive heater 300 from handlingdamage and spring damage. The heater backing plate 350 acts as a heatcarrier for the resistive heater 300 providing a certain thermalgradient across the resistive heater 300. The heater backing plate 350provides a means to attach the resistive heater 300 to other parts in anassembly. The preferred method of attaching the heater backing plate 350to the resistive heater 300 by a vulcanization process. Thevulcanization process provides a reliable attachment method with lessdegradation, over time, as compared with many adhesive attachmentmethods. Vulcanization is a chemical curing of the rubber insulationthat is attached to the heater backing plate 350 that provides anadvantage of a more reliable connection between the heater backing plate350 and the resistive heater 300. Vulcanization not only ensures auniform and reliable connection, but helps provide a more reliableproduct for a entire service life which involves repeated thermalcycling. Other attachment methods that could be used to attach theheater backing plate 350 to the resistive heater 300 include, but arenot limited to, adhesives, pressure sensitive adhesives (PSA),mechanical fasteners, and other similar materials. Many types ofpressure sensitive adhesives (PSA) could be used to attach to attach theheater backing plate 350 to the resistive heater 300. Those skilled inthe art will recognize that other methods of attaching known in the artwould be within the spirit and scope of the present invention.

[0130] Prior art thermal systems do not have consistent, uniform thermalcontact between the sample well caps and the heater. Inconsistent andnon-uniform contact between the caps and the heater can causeinefficiencies and inaccurate results. The flexible heater coverassembly 200 of the present invention has the heater backing plate 350helps the plate and heater assembly (FIGS. 29-32) to better contact thesurface of the sample tube caps 146. The sample tube caps 146 may varyin installed height, either from tube height differences, thermal systembase 15 well height differences, or cap thickness differences. Thesample tube caps 146 also may be installed on the tubes in a non-uniformmanner. The sample tube caps 146 may be not fully seated onto the tube,or they may be twisted such that the top horizontal surface of thesample tube cap 146 is not positioned in a horizontal plane. Thesedifferences create a design challenge for getting a consistent, uniformthermal contact between the resistive heater 300 and the sample tubecaps 146. The flexibility of the heater backing plate 350 minimizes thisproblem by allowing flexible, consistent, uniform thermal contact forall 96 sample wells caps 146.

[0131] The preferred surface treatment of the top surface of the heaterbacking plate 350 is to coat the top surface of the heater backing plate350 with a black dye through an anodization process. The black dye isadded into the anodization bath because the black dye leaves the topsurface of the heater backing plate 350 with a black color that is apoor optical reflector so that top surface does not reflect or scatterlight from the area above one well to other adjacent wells. Anyreflection or scattering of light from one well to another wellcontributes to optical cross-talk and decreases the quality of theoptical data. The preferred black anodized top surface of the heaterbacking plate 350 helps to minimize optical signal background noise andscattering (signal reduction) because the black surface is lessreflective in the wavelengths commonly associated with fluorescent dyesused in PCR. Many other surface treatment could be used within thespirit and scope of the present invention. Other surface treatments thatcould be used include, but are not limited to, natural coloranodization, colored anodizations, chemical conversion film coatings andsimilar surface treatments. The natural color anodization leaves the topsurface of the plate with its natural color, light olive to gray. Thenatural color anodization is simpler than cheaper than the preferredblack dye anodization process because no dye is used in the naturalcolor anodization process. In colored anodizations, the top surface ofthe plate takes on the color of a dye that is added during theanodization process. The chemical conversion film coating provides amild surface protection and is widely used to treat aluminum. Thoseskilled in the art will recognize that other surface treatments known inthe art would be within the spirit and scope of the present invention.The anodized surface also provides a more wear resistant surface tointerface with a series of springs located above the heater backingplate 350. The springs contact the surface of the heater backing plate350 and slide along the surface during loading and unloading of thesample tubes 140 as will now be discussed.

[0132] As shown in FIGS. 33-35, the flexible heating cover assembly 200includes a plurality of spring strips 400. The spring strips 400 arelocated above the heater backing plate 350. In combination with thestiff support plate 500, the spring strips 400 provide a spring force tothe resistive heater 300 which is distributed about the resistive heater300 and the plurality of sample wells. The spring strips 400 includes anelongated body 402, a curved retainer lip 404, and a plurality of springextensions 406 having an extension end 408.

[0133] In the present invention, the spring strips 400 act as cantileversprings. The spring strip 400 has a plurality of spring points. A springpoint is the area of contact between the extension end 408 of the springextension 406 and the heater backing plate 350 attached to the resistiveheater 300. Each spring point corresponds to the spring extension 406having an extension end 408. In a preferred embodiment of the presentinvention, the spring strip 400 has nine spring points which interfacewith the heater backing plate 350 attached to the resistive heater 300.The nine spring points of each spring strip 400 are spaced such thateach spring point is located approximately half way between adjacentsample well centers. Thus, there is a consistent force applied to theheater backing plate 350 attached to the resistive heater 300 about eachsample well. In other embodiments of the present invention, the springstrip 400 may have more or less than nine spring points (i.e., fivespring points, eight spring points, ten or more spring points). Becauseeach spring strip 400 preferably contains nine spring points (and ninespring extensions 406 that each act a spring), only a limited number ofspring strips 400 need to be installed to provide a spring-like forcebetween each of the plurality of sample wells. In a preferred embodimentof the present invention, 13 spring strips 400 are used, providing 117spring points that can apply force to the heater backing plate 350attached to the resistive heater 300. In other embodiments of thepresent invention, any number of spring strips 400 may be used toprovide various force levels (i.e., five spring strips, ten springstrips, fifteen or more spring strips). The number and location ofspring strips 400 used can vary to provide various force levels on theheater backing plate 350 attached to the resistive heater 300.

[0134] The spring force of the spring strips 400 is transferred from theextension end 408 of the spring extensions 406 to the heater backingplate 350 attached to the resistive heater 300. Each spring extensions406 acts as a cantilevered spring to transfer the spring force. Thespring strips 400 are configured such that the spring force is appliedat the spring point between the hole centers of adjacent sample wells.For example, if there are four of the sample well holes in the centralportion of the heater backing plate 350 attached to the resistive heater300, the spring force points would be roughly located between the foursample wells. The spring force is not applied between two of the samplewell holes in the heater backing plate 350 attached to the resistiveheater 300 (either two columns or two rows); the spring force is appliedbetween all four adjacent sample wells.

[0135] The preferred material of spring strips 400 is beryllium copper.Many other materials could be used within the spirit and scope of thepresent invention. Other materials of the spring strips 400 that couldbe used include, but are not limited to, stainless steel, carbon steeland similar materials. Those skilled in the art will recognize thatother spring materials known in the art would be within the spirit andscope of the present invention. The preferred thickness of the springstrip 400 is 0.004 inches, although those skilled in the art willrecognize that other thicknesses would be within the spirit and scope ofthe present invention. The preferred length of the spring strip isslightly longer than the column of sample well holes, although thoseskilled in the art will recognize that other lengths would be within thespirit and scope of the present invention. The spring strips 400 arecost effectively produced from a sheet of metal by laser cutting theelongated body 402, bending up or stamping the plurality of springextensions 406, and heat treating the metal to the proper temper.

[0136] The spring strips 400 are designed to provide from about 10 gramsto about 30 grams of force for each sample tube. Each spring extension406 helps to create about 10 grams to about 30 grams of force for eachsample well. Each spring extension 406 does not provide about 10 gramsto about 30 grams of force itself, but helps to create about 10 grams toabout 30 grams of force for each sample well. The spring strips 400 andthe heater backing plate 350 attached to the resistive heater 300combine to provide this force more uniformly for each sample tube ascompared to prior art. Thus, the spring strips 400 are an improvementover installing a separate conventional spring between each of the 96holes because the spring strips 400 use fewer parts and impart a moreuniform force.

[0137] In the prior art, the heating cover was not flexible and did notpromote load sharing, thus the sample tubes and sample caps that weretaller would receive a higher force while the sample tubes and caps thatwere lower would receive a lesser force. The uneven force distributionin the prior art lead to inefficiencies and inaccurate results. Whilemany prior art products employ a design which concentrates most of theforce onto a subset of sample tubes, the design of the present inventionprovides superior load sharing among sample tubes through the enhancedflexibility of the heater assembly.

[0138] The flexible heating cover assembly 200 of the present inventionprovides more uniform load sharing among the sample tubes throughenhanced flexibility. Because the heater backing plate 350 attached tothe resistive heater 300 has a stiffness and because of the location andforce of the spring strips 400, the flexible heater cover assembly 200of the present invention provides a flexible heater that promotes betterand more uniform contact with each sample cap, even if the sample capsare distorted, twisted, at slightly different elevations, or atdifferent angles relative to the horizontal plane. Because all sampletubes and sample caps will be at slightly different heights, the load oneach sample tube will be non-uniform and different. Due to theflexibility and resulting distribution of force of the presentinvention, there is less of a force increase on the taller sample tubesand caps, and a smaller force differential on shorter sample tubes andcaps. An advantage of the load sharing design of the present inventionis a reduced risk of sample tube or sample cap damage (and biologicalmaterial contamination) from too much force imparted onto a few sampletubes or sample caps. Another advantage of the load sharing design ofthe present invention is a more uniform force in a vertical directionfor each sample tube so that a more uniform thermal resistance path iscreated between the conical wall of the sample tube and the sample wellwall of the thermal system base 15 which results in better thermaluniformity among biological samples. Another advantage of the loadsharing design of the present invention is that flat or domed samplecaps may be used to provide flexibility in optimizing the opticalproperties of the radiation path. Another advantage of the load sharingdesign of the present invention is that robotic loading and unloading ofsample tubes is promoted due to the lower overall force and due to theelimination of damaged tube caps. The load sharing of the presentinvention helps to yield more accurate results and increase efficiency.Those skilled in art will recognize these advantages and otheradvantages of the flexible load sharing design of the present invention.

[0139] Although the spring strips 400 act as cantilever springs, manyother spring designs could be used within the spirit and scope of thepresent invention. Other spring designs that could be used include, butare not limited to, a compression spring, a circular spring, a wavewasher-type spring, a conical spring, a Belleville spring/washer andsimilar springs. Compression springs are open-coiled helical springsthat offer resistance to compressive forces applied axially. Suchsprings are usually coiled as a constant diameter cylinder; other commonforms are conical, tapered, concave, convex, and combinations of these.Most compression springs are manufactured in round wire because thisoffers the best performance and is readily available and suited tostandard coiler tooling—but square, rectangular, or special-section wirecan be specified. A wave washer-type spring is basically a circularspring that has a different inside coil diameter and an outside coildiameter and the spring may be wavy as you work your way around theperimeter to create a spring. The inside coil diameter of a spring isthe diameter of the cylindrical envelope formed by the inside surface ofthe coils of a spring. The outside coil diameter of a spring is thediameter of the cylindrical envelope formed by the outside surface ofthe coils of a spring. A Belleville spring, disc spring, conicalcompression washer are all names for the same type of spring. ABelleville spring, also called Belleville washer, is a conical diskspring. The load is applied on the periphery of the circle and supportedat the bottom. Belleville springs are used in a variety of applicationswhere high spring loads are required. Belleville springs areparticularly useful where vibration, differential thermal expansion,relaxation, and bolt creep are problems. A Belleville spring washer is awasher in the form of a cone, of constant material thickness, used as acompression spring. Unlike compression springs, Belleville springwashers can accommodate exceptionally high loads in restricted spaces.Those skilled in the art will recognize that other springs known in theart would be within the spirit and scope of the present invention.

[0140] As shown in FIGS. 36 and 37, the spring retainer plate 450includes a plurality of sample well holes 452, a plurality of slots 454,a plurality of notched corner 456, a plurality of securing holes 458,and a top surface 460. The spring retainer plate 450 is used to retainthe plurality of spring strips 400. The spring retainer plate 450contains the plurality of slots 454 that allows the plurality of springextensions 406 of each spring strip 400 to pass through the springretainer plate 450. In assembly of the flexible heating cover of thepresent invention, the spring strip 400 is placed above the top surface460 of the spring retainer plate 450 and the spring strip 400 is loweredso that the spring extensions 406 of each spring strip 400 pass throughthe plurality of slots 454 of the spring retainer plate 450. The springstrip 400 is lowered until the elongated body 402 of each spring strip400 engages the top surface 460 of the spring retainer plate 450. Thespring retainer plate 450 retains the spring strips 400 in the verticaldirection and also provides a mechanical stop to prevent over travel foreach spring strip 400. Such over travel could yield the spring materialand degrade the force applied to the heater backing plate 350 attachedto the resistive heater 300. The spring retainer plate 450 also containsthe a plurality of notched corner 456 which allow for easiermanipulation of the spring retainer plate 450 during assembly of thespring retainer plate 450.

[0141] In a preferred embodiment of the present invention, the springretainer plate 450 is are composed of aluminum alloy 1100 with a temperdesignation of H12 or H14. Other aluminum alloys that could be usedwithin the spirit and scope of the present invention include, but arenot limited to, aluminum 6061, aluminum 6063, and similar aluminumalloys. Aluminum alloy 6061 is a common form of aluminum and has a widerang of uses. Aluminum alloy 6063 is an architectural grade of aluminumthat is widely used in industry. Those skilled in the art will recognizethat other aluminum alloys known in the art would be within the spiritand scope of the present invention. In addition, other similar materialsthat could be used include, but are not limited to, polycarbonate (PC)(common trade names include lexan), polyetherimide (PEI) (common tradenames include ultem), and similar materials. Those skilled in the artwill recognize that other materials and alloys known in the art would bewithin the spirit and scope of the present invention.

[0142] The plurality of securing holes 458 of the spring retainer plate450 allow for mechanical attachment of the spring retainer plate 450 tothe stiff support plate 500 with common fasteners placed through theplurality of securing holes 458. The preferred method of attaching thespring retainer plate 450 to the stiff support plate 500 is by screwingusing common small screws. Other attachment methods that could be usedfor the attaching the spring retainer plate 450 to the stiff supportplate 500 include, but are not limited to, adhesives, glues, rivets,blind fasteners, mechanical snapping and other mechanical fasteners.Those skilled in the art will recognize that other methods of attachingthe spring retainer plate 450 to the stiff support plate 500 known inthe art would be within the spirit and scope of the present invention.

[0143] As shown in FIGS. 38 and 39, the stiff support plate 500 includesa plurality of sample well holes 502, a top surface 504, a bottomsurface 506, a plurality of spring slots 508, and a plurality of ribs510. The stiff support plate 500 is used to provide stiffness for thespring strips 400. The plurality of sample well holes 502 in the stiffsupport plate 500 permit emitted radiation to pass through the holes 502to reach optical scanning equipment that collects optical data collectedfor quantitative PCR type experiments.

[0144] As best shown in FIG. 39, the plurality of spring slots 508 arelocated on the bottom surface 506 of the stiff support plate 500. Thespring slots 508 act to locate the spring strips 400 in the horizontalplane and the bottom of the spring slots 508 act to locate the springstrips 400 in at least partially in the vertical direction. Preferably,the stiff support plate 500 contains the spring slots 508 for 13 springstrips 400, those skilled in the art will recognize the any number ofthe spring slots 508 could be machined in the bottom surface 506 of thestiff support plate 500 for use with alternate configurations of springstrips 400 discussed above.

[0145] The performance objectives of the stiff support plate 500include, but are not limited to, the following: (1) a stiffnessmeasure—a force versus deflection profile across the stiff support plate500; (2) a stiff support plate 500 thickness that would effect thestiffness and also affect the optical sensitivity. The stiffness of thestiff support plate 500 is sufficient to provide a reaction force forall spring strips with minimal deflection of the stiff support plate500. In this manner, the stiff support plate 500 retains its nearlyplanar shape under loading force from the spring strips 400, while theloading force from the bottom side of the spring strips 400 act todeform the heater backing plate 350 attached to the resistive heater300.

[0146] As best shown in FIG. 38, the plurality of ribs 510 are locatedon the top surface 506 of the stiff support plate 500. The plurality ofribs 510 provide stiffness to the stiff support plate 500 whilepermitting the close travel of optical scanning equipment to passbetween the ribs 510. The optical scanning equipment can move in a nearconstant velocity scanning motion or a point-to-point, move and hovertype scanning motion to promote the emission and collection of radiationinto and out of the flexible heating cover assembly 200 and the sampletubes 140. The close travel of the optical scanning equipment to thestiff support plate 500 promotes the sensitivity of the optical datacollected for quantitative PCR type experiments. The rib 510orientation, quantity, thickness and height all would play intostiffness and would also be specific to the method of optical datacollection (i.e., scanning or some other type of optical datacollection). In an alternative embodiments of the present inventionwhere an optical detector is placed above each of the sample wells 24(instead of optically scanning) then the ribs 510 would not be necessaryand a cavity or a counter bore around each of the sample wells 24 wouldsuffice. In other alternative embodiments of the present invention usingdifferent scanning approaches, many combinations of the physicalparameters of the stiff support plate 500 could be varied to achieve itsperformance. For example, with a smaller force range (about 10 to about16 grams per well), the stiff support plate 500 could be optimized bydecreasing the stiffness of the stiff support plate 500 and gaining someoptical sensitivity. Thus, the optical sensitivity could be enhanced atthe expense of some of the stiffness with a smaller force range.

[0147] Preferably, the stiff support plate 500 is composed of aluminumalloy 6061-T6. Many other materials with sufficient stiffness could beused within the spirit and scope of the present invention. Othermaterials that could be used to fabricate the stiff support plate 500include, but are not limited to, other aluminum alloys (1100, 6063,5032), polyetherimide (PEI) (common trade names include ultem),titanium, titanium alloys, stainless steel, carbon steel,beryllium-aluminum alloys, and similar materials. Beryllium-aluminumalloys are fairly rare and can be easily cast and retain exceptionalstiffness versus weight properties. Beryllium-aluminum alloys may beused as a cast part for the stiff support plate to keep the fabricationcost low, while providing an optical sensitivity advantage by making thestiff support plate thinner, or reducing the rib height, or deleting theribs. Stainless steel or carbon steel have a modulus of the materialthat would yield a stiffer stiff support plate 500. Titanium has about50% better stiffness than aluminum, but has about 50% more weight thanaluminum. Those skilled in the art will recognize that other materialsknown in the art would be within the spirit and scope of the presentinvention. The stiff support plate 500 is preferably 0.130 inches thickthrough a section between the ribs 510. The ribs 510 preferably extend0.165 inches above the top of the stiff support plate 500. The preferredrib thickness is 0.048 inches. Those skilled in the art will recognizethat other combinations of rib height, rib thickness, rib quantity, riborientation, and plate thickness, size, and material, are within thespirit and scope of the invention.

[0148] The stiff support plate 500 is also coated with a black dyethrough an anodization process to minimize optical signal backgroundnoise and scattering (signal reduction). The black dye is added into theanodization bath because the black dye leaves the stiff support plate500 with a black color that is a poor optical reflector so that topsurface does not reflect or scatter light from the area above one wellto other adjacent wells. Any reflection or scattering of light from onewell to another well contributes to optical cross-talk and decreases thequality of the optical data. The preferred black anodized top surface ofthe stiff support plate 500 helps to minimize optical signal backgroundnoise and scattering (signal reduction) because the black surface isless reflective in the wavelengths commonly associated with fluorescentdyes used in PCR. Many other surface treatment could be used within thespirit and scope of the present invention. Other surface treatments thatcould be used include, but are not limited to, natural coloranodization, colored anodizations, chemical conversion film coatings andsimilar surface treatments. The natural color anodization leaves the topsurface of the plate with its natural color, light olive to gray. Thenatural color anodization is simpler than cheaper than the preferredblack dye anodization process because no dye is used in the naturalcolor anodization process. In colored anodizations, the top surface ofthe plate takes on the color of a dye that is added during theanodization process. The chemical conversion film coating provides amild surface protection and is widely used to treat aluminum. Thoseskilled in the art will recognize that other surface treatments known inthe art would be within the spirit and scope of the present invention.

[0149] The stiff support plate 500 also contains other mechanicalfeatures which can be used to attach various skirt components 250 toachieve an ambient environment around the upper portion of the sampletubes 140 and sample tubes caps 146 which is favorable. The stiffsupport plate 500 and various skirt components 250 minimize theconvective heat loss and minimize any convective air flow disruptionswhich could degrade the target temperature of the flexible heaterassembly 200 or the thermal system base 15.

[0150] As shown in FIGS. 40 and 41, the flexible heater cover assembly200 of the present invention includes a plurality of heater slides 550.The heater slide 550 is used to locate and guide the heater backingplate 350 attached to the resistive heater 300 within the coverassembly. The heater slide 550 controls the heater backing plate 350attached to the resistive heater 300 position in the horizontal plane,while permitting some freedom of movement in the vertical direction witha minimum reaction force from friction imparted to the heater backingplate 350 attached to the resistive heater 300. The heater slide 550interfaces with a slot along the outer edges of the heater backing plate350 attached to the resistive heater 300.

[0151] The flexible heater cover assembly 200 of the present inventionincludes a plurality of heater slides 550. In a preferred embodiment ofthe present invention, four heater slides 550 are used. The four heaterslides 550 are located about the heater backing plate 350 attached tothe resistive heater 300 in a symmetrical manner relative to theplurality of sample well holes 312, 352. In this way, the thermal effectfrom the contact of the heater slides 550 is symmetrical so that anyimpact to the temperature gradient about the heater backing plate 350attached to the resistive heater 300 is symmetrical to the plurality ofsample well holes 312, 352. In other embodiments of the presentinvention, any number of heater slides 550 could be used (i.e., oneheater slide, two heater slides, three heater slides, or five or moreheater slides). In embodiments of the present invention using more orless than fours heater slides 550, the size, shape, orientation andconfiguration of the heater slides may be modified. For example, in anembodiment of the present invention that uses two heater slides, theheater slides my be very long. Those skilled in the art will recognizethat other sizes, shapes, quantities, orientations and configurations ofthe heater slides 550 could be used within the spirit and scope of theinvention.

[0152] The heater slide 550 should be shaped to have a minimal contactwith the heater backing plate 350 attached to the resistive heater 300so the desired non-uniform heat distribution is maintained. In apreferred embodiment of the present invention, the heater slide 550 isU-shaped. Many other shapes of the heater slides 550 could be usedwithin the spirit and scope of the present invention. Other shapes ofthe heater slides 550 include, but are not limited to, a rectangularblock, a cylinder, a stretched shape that is long and thin, and othersimilar shapes. Those skilled in the art will recognize that othershapes known in the art would be within the spirit and scope of thepresent invention.

[0153] Preferably, the heater slide 550 is composed of acetal, a plasticmaterial. Acetals, technically polyoxymethylenes (POM), are highlycrystalline engineering thermoplastic resins. Acetal is commerciallyavailable under the common trade name include delrin. Acetal performancecharacteristics combine high strength and rigidity, unusual resilience,outstanding static and dynamic fatigue resistance, natural lubricity,and resistance to a wide range of solvents, oils, greases and chemicals.Very low moisture absorption results in excellent dimensional stability,and maintenance of performance characteristics over a wide range ofhumidity. Many other materials with similar low friction propertieswhile subjected to a PCR temperature environment around 100° C. forextended time periods could be used within the spirit and scope of thepresent invention. Other materials having similar characteristics ofexcellent mechanical, thermal and chemical properties, wide range oftemperature for an extended period, good self-lubrication,friction-resistance and abrasion-resistance, high rigidity andconductivity could be used to fabricate the stiff plate include, but arenot limited to, Acrylonitrile-Butadiene-Styrene (ABS), otherstyrene-based materials, polyvinylchloride (PVC), polyamide (commontrade names include zytel and nylon), polypropylene, vinyl,polycarbonate, polytetrafluoroethylene (PTFE) (common trade namesinclude teflon), pet, pbt, tpr, tpe, acrylic, polystyrene, otherplastics, titanium, titanium alloys, stainless steel, carbon steel andsimilar materials. Styrene-based materials offer unique characteristicsof durability, high performance, versatility of design, simplicity ofproduction, and economy and provide excellent hygiene, sanitation, andsafety benefits. Those skilled in the art will recognize that othermaterials known in the art would be within the spirit and scope of thepresent invention.

[0154] The means for attaching the various components of the flexibleheater cover assembly 200 will now be described. It is important thatthe means for attaching the various components does not result insignificant heat transfer away. The attachment fasteners attach thecover assembly skirt 250, the resistive heater 300, the heater backingplate 350, the spring strip 400, the spring retainer plate 450, thestiff support plate 500, and the plurality of heater slides 550. Theaforementioned components engage each other to form the flexible heatingcover assembly 200. The attachment fasteners have been designed tominimize the heat transfer that occurs through the attachment fasteners.It should be understood that any attachment fasteners known in the artmay be used including, but not limited to, screws, nuts and bolts,rivets, welds, adhesives, and other mechanical connectors.

[0155] The flexible heating cover assembly 200 requires a means whichacts as a clamping function between the flexible heating cover assembly200 and the thermal system base 15. The clamping function should provideat least three important characteristics. First, the clamping functionshould sufficiently generate a clamping force which is greater inmagnitude than the total force created by the spring force system in theflexible heating cover assembly which imparts force into the sampletubes 140 and sample tube caps 146 and into the thermal system base 15.Second, the clamping function should generate the force in a directionwhich is nearly vertical, or the vertical component of a force which isnot vertical must have a magnitude which satisfies the first clampingfunction characteristic. Also, the nearly vertical force or component ofa non-vertical force must be directed downward, assuming that theposition of the thermal system base 15 is below the flexible heatingcover assembly 200. Third, the clamping function should apply the forcein a plurality of locations. In a preferred embodiment of the presentinvention, the force is applied at four locations. The four forcelocations are approximately about each corner of the flexible heatingcover assembly 200: front left corner, front right corner, rear leftcorner, and rear right corner. In an alternative embodiment of thepresent invention, two force locations may be employed. For example, amanually operated instrument sample loading scheme could have two forcelocations. In the alternative embodiment having two force locations, afirst force location would preferably be located along the left side ofthe flexible heating cover assembly 200, about midway front to back. Asecond force location would preferably be located along the right sideof the flexible heating cover assembly 200, about mid way front to back.For the two force location embodiment, the interfacing locations on theflexible heating cover assembly 200 structure would be revised such thattheir numbers and locations would be consistent with the two forcelocation embodiment. The details of a mechanism or a manual clamp toaccomplish the clamping function are known to those skilled in the art.Mechanisms for accomplishing the clamping function include, but arelimited to, a manual lever or clamp, an automated lever or clamp, alatch mechanism, a spring over center design. Those skilled in the artwill recognize that a variety of clamping function designs could beemployed to satisfy the needs of the flexible heating cover assembly 200are be within the spirit and scope of the present invention.

[0156] The operation of the flexible heating cover assembly 200 attachedto the thermal system base 15 will be described below. The flexibleheating cover assembly 200 of the present invention is opened up bypivoting about hinges. A tray of disposable sample tubes 140 are placedso that the sample tubes 140 are positioned in the sample wells 24. Theflexible heating cover assembly 200 is then closed.

[0157] Thermal cycling can now be performed. The thermal cycling iscontrolled by a controller. During thermal cycling, the DNA will undergoa pre-programmed thermal cycling process of raising and loweringtemperatures in order to replicate the strands of DNA. Before undergoingthe process, the temperature of the thermal block assembly 20 ismeasured at at least one location. The controller then calculates thedesired temperature of the thermal block assembly 20 at the particulartime. The desired temperature is then compared to the measuredtemperature. If the measured temperature is less than the desiredtemperature, heating of the thermal block assembly 20 will occur.Heating the thermal block assembly 20 comprises several steps. The firststep is imparting a first heat rate via at least one first heater, aportion of the first heat rate being transferred to the thermal blockassembly 20. The second step is imparting a second heat rate via asecond heater, a portion of the second heat rate being transferred tothe first heater. The third step is imparting a third heat rate via athird heater, a portion of the third heat rate being transferred to thetop of the sample tubes in order to reduce the likelihood ofcondensation occurring on the top of sample tubes. It is understood thatall three of these steps may be performed simultaneously.

[0158] Because a plurality of first heaters may be provided, the heatrate output of each of the plurality of first heaters may beindependently controlled. This will allow the controller to monitor thesensor cup temperatures so that all of the sensor cups have asubstantially equal temperature. Likewise, if a plurality of secondheaters is provided, the heat rate output of each of the second heatersmay also be independently controlled.

[0159] However, if the measured temperature is greater than the desiredtemperature, heating does not occur but instead the thermal blockassembly will be cooled. This is done by reversing the current on thePeltier heaters 40 in order to turn them into coolers, and by alsoimparting a cooling convection current on the heat sink which isthermally coupled to the thermal block assembly to provide heat transferfrom the thermal block assembly to ambient air adjacent the heat sink. Aradial fan may be provided for providing the convection current to theheat sink.

[0160] Once the step of heating or cooling is performed, the cyclecontinues by repeating the steps of measuring, calculating, andcomparing until the predetermined thermal cycle for the samples ofbiological reaction mixture is completed. After the proper number ofcycles have been performed, the flexible heating cover assembly 200 willbe opened and the DNA sample tubes will be removed from the samplewells.

[0161] The thermal system base 15 could also be modified to incorporatea temperature gradient means across the thermal block assembly 20. Athermal system base 15 with a temperature gradient means is used todiscover the optimum polymerase chain reaction annealing stagetemperatures. The thermal system base 15 is primarily focused towardsproducing the DNA via polymerase chain reactions once these temperaturesare known. However, the thermal system base 15 could be modified toinclude a temperature gradient means or independent temperature zones.

[0162] The flexible heating cover assembly 200 of the present inventionprovides superior multiplexing performance, increases throughput,decreases reagent costs, allows more stringent control protocols,expands data analysis and display options, provides ease of use andflexibility, safeguards the data, increases reliability, and decreasesmaintenance and service. The flexible heating cover assembly 200 of thepresent invention is also compatible with numerous fluorescentchemistries (i.e., primers, probes, dyes, and the like).

[0163] The flexible heating cover assembly 200 when used in conjunctionwith the thermal system base 15 is advantageous over the prior art forits precision, speed, and uniformity. The flexible heating coverassembly 200 is precise because the cycling temperatures of the sampleblock are regulated by a hybrid system of Peltier, resistive, andconvective technologies for tight temperature control. The flexibleheating cover assembly 200 is fast because design features of the sampleblock increase the thermal ramping rate. For example, a forty-cycle QPCRprotocol can be completed in less than one and one-half hours. Theflexible heating cover assembly 200 provides uniformity because thethermal cycler has unparalleled thermal accuracy—about ±0.25° C.variation in sample temperature across the 96-well plate for optimalcycling conditions.

[0164] The flexible heating cover assembly 200 when used in conjunctionwith the thermal system base 15 requires no additional pipetting orhandling of samples because amplification and detection occur in thesame sample tube. The thermal plate holds reactions in a standard96-well format, for high throughput of samples. Reactions are cycledwithin well-controlled temperature specifications that avoid reductionof enzyme half-life and non-specific PCR product formation. Idealtemperature conductivity is achieved through the cone-shaped geometricdesign of the sample wells. The design not only maximizes contactbetween the sample wells and thermal block it also minimizes mass forhigh-speed thermal ramping.

[0165] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the design and constructionof the flexible heater cover assembly of the present invention withoutdeparting from the scope or spirit of the invention.

[0166] All patents, patent applications, and published references citedherein are hereby incorporated by reference in their entirety. Whilethis invention has been particularly shown and described with referencesto preferred embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the scope of the invention encompassed by theappended claims.

What is claimed is:
 1. A flexible heating cover assembly comprising: ahousing including a plurality of engageable enclosure components; aresistive heater located within the housing, the resistive heaterincluding a plurality of heater element areas; a heater backing plateengaging the resistive heater and providing stability to the resistiveheater; a force distribution system that engages the heater backingplate and distributes a force over the heater backing plate; and asupport plate providing stiffness for the force distribution system,wherein the arrangement of the resistive heater, the heater backingplate, the force distribution system and the support plate providesubstantial temperature uniformity among a plurality of sample tubes forreceiving samples of biological material.
 2. The flexible heating coverassembly of claim 1 wherein the housing further comprises a pair of endcaps and a pair of side bars all composed of a thermally insulatingmaterial.
 3. The flexible heating cover assembly of claim 1 wherein theresistive heater is thin to allow rapid heating and cooling duringthermal cycling of the plurality of sample tubes.
 4. The flexibleheating cover assembly of claim 1 wherein the resistive heater producesa non-uniform heat distribution along a surface exposed to the pluralityof sample tubes.
 5. The flexible heating cover assembly of claim 1wherein the resistive heater further comprises a plurality of heaterelement areas including at least one outer heater element area and atleast one central heater element area.
 6. The flexible heating coverassembly of claim 5 wherein the at least one outer heater element areais C-shaped and located along an outer edge of a plurality of samplewell openings.
 7. The flexible heating cover assembly of claim 5 whereinthe at least one outer heater element area includes a tapered portionand curved end portions.
 8. The flexible heating cover assembly of claim1 wherein the resistive heater further comprises at least one heatcarrier circuit that is not electrically connected to a heater powersource wherein the at least one heat carrier circuit transfers heaterthrough the resistive heater.
 9. The flexible heating cover assembly ofclaim 1 wherein the resistive heater further comprises a thermistorlocated toward a center portion of the resistive heater to providecontrol of the vapor and the condensation environment of the pluralityof sample tubes.
 10. The flexible heating cover assembly of claim 1wherein the resistive heater can move vertically within the flexibleheating cover assembly to provide a more uniform heat distribution. 11.The flexible heating cover assembly of claim 1 wherein the heaterbacking plate is thin to promote flexibility when the heater backingplate is connected to the resistive heater.
 12. The flexible heatingcover assembly of claim 1 wherein the heater backing plate is composedof a thermally conductive material.
 13. The flexible heating coverassembly of claim 1 wherein the heater backing plate further comprises aplurality of narrow slots to promote the flexibility of the heaterbacking plate and minimize the retardation of heat transfer through theheater backing plate.
 14. The flexible heating cover assembly of claim 1wherein a top surface of the heater backing plate is treated to minimizereflecting or scattering of light from the top surface of the heaterbacking plate.
 15. The flexible heating cover assembly of claim 1wherein the force distribution system further comprises at least onespring strip and a spring retainer plate.
 16. The flexible heating coverassembly of claim 15 wherein the at least one spring strip has anelongated body and a plurality of spring extensions.
 17. The flexibleheating cover assembly of claim 16 wherein the plurality of springextensions distribute the force uniformly on the heater backing plate.18. The flexible heating cover assembly of claim 16 wherein the springretainer plate retains the at least one spring strip and allows theplurality of spring extensions of the at least one spring strip to passthrough the spring retainer plate.
 19. The flexible heating coverassembly of claim 1 wherein the support plate has sufficient stiffnessto provide a reaction force for the force distribution system withminimal deflection of the support plate.
 20. The flexible heating coverassembly of claim 1 wherein the support plate retains a substantiallyplanar shape under a loading force from the force distribution system,while the loading force acts to deform the heater backing plate attachedto the resistive heater.
 21. The flexible heating cover assembly ofclaim 1 wherein the support plate has a plurality of ribs located on atop surface of the support plate to provide stiffness to the supportplate while permitting the close travel of optical scanning equipment topass between the plurality of ribs.
 22. The flexible heating coverassembly of claim 1 further comprising at least one heater slide tolocate and guide the heater backing plate attached to the resistiveheater in the flexible heating cover assembly.
 23. The flexible heatingcover assembly of claim 1 wherein at least one heater slide controls ahorizontal position of the heater backing plate attached to theresistive heater, while permitting some freedom of movement in avertical direction.
 24. The flexible heating cover assembly of claim 1wherein the resistive heater, the heater backing plate, and the supportplate each comprise a plurality of aligned sample well openings, eachsample well opening corresponding to a respective sample tube of theplurality of sample tubes.
 25. The flexible heating cover assembly ofclaim 1 further comprising an optical scanning equipment that collectsoptical data for quantitative PCR type experiments.
 26. The flexibleheating cover assembly of claim 1 wherein a plurality of mechanicalinterfaces transfer force between the flexible heating cover assemblyand a thermal system base.
 27. The flexible heating cover assembly ofclaim 1 wherein the flexible heating cover assembly surrounds the topand extends over at least a portion of a side of a thermal system base.28. The flexible heating cover assembly of claim 1 wherein the flexibleheating cover assembly holds the plurality of sample tubes in aplurality of sample wells of a thermal system base by imparting asubstantially uniform compressive force on the plurality of sampletubes.
 29. The flexible heating cover assembly of claim 1 wherein theflexible heating cover assembly tends to thermally insulate theplurality of sample tubes.
 30. The flexible heating cover assembly ofclaim 1 wherein each sample tube extends for a substantial length in theflexible heating cover assembly.
 31. The flexible heating cover assemblyof claim 1 wherein the flexible heating cover assembly is capable ofwithstanding thermally cycling of the samples of biological material.32. The flexible heating cover assembly of claim 1 wherein the flexibleheating cover assembly helps to minimize the convective heat loss to anambient environment.
 33. A cover assembly for an apparatus for heatingsamples of biological material, comprising: a housing including aplurality of engageable enclosure components; a resistive heater locatedwithin the housing, the resistive heater including at least one outerheater element area and at least one central heater element area; aheater backing plate engaging the resistive heater to provide protectionand stability to the resistive heater, wherein the heater backing plateis thin and composed of a thermally conductive material; a forcedistribution system comprising at least one spring strip and a springretainer plate, the force distribution system engaging the heaterbacking plate to distribute a force over the heater backing plate; and asupport plate providing sufficient stiffness to provide a reaction forcefor the force distribution system with minimal deflection of the supportplate, wherein the arrangement of the resistive heater, the heaterbacking plate, the force distribution system and the support plateprovide substantial temperature uniformity among a plurality of sampletubes for receiving samples of biological material.
 34. The coverassembly of claim 33 wherein the housing further comprises a pair of endcaps and a pair of side bars all composed of a thermally insulatingmaterial.
 35. The cover assembly of claim 33 wherein the resistiveheater is thin to allow rapid heating and cooling during thermal cyclingof the plurality of sample tubes.
 36. The cover assembly of claim 33wherein the resistive heater produces a nonuniform heat distributionalong a surface exposed to the plurality of sample tubes.
 37. The coverassembly of claim 33 wherein the at least one outer heater element areais C-shaped and located along an outer edge of a plurality of samplewell openings.
 38. The cover assembly of claim 33 wherein the at leastone outer heater element area includes a tapered portion and curved endportions.
 39. The cover assembly of claim 33 wherein the resistiveheater further comprises at least one heat carrier circuit that is notelectrically connected to a heater power source wherein the at least oneheat carrier circuit transfers heater through the resistive heater. 40.The cover assembly of claim 33 wherein the resistive heater furthercomprises a thermistor located toward a center portion of the resistiveheater to provide control of the vapor and the condensation environmentof the plurality of sample tubes.
 41. The cover assembly of claim 33wherein the resistive heater can move vertically within the flexibleheating cover assembly to provide a more uniform heat distribution. 42.The cover assembly of claim 33 wherein the heater backing plate furthercomprises a plurality of narrow slots to promote the flexibility of theheater backing plate and minimize the retardation of heat transferthrough the heater backing plate.
 43. The cover assembly of claim 33wherein a bottom surface of heater backing plate is connected to theresistive heater to provide protection and stability to the resistiveheater.
 44. The cover assembly of claim 33 wherein a top surface of theheater backing plate is treated to minimize reflecting or scattering oflight from the top surface of the heater backing plate.
 45. The coverassembly of claim 33 wherein the at least one spring strip has anelongated body and a plurality of spring extensions.
 46. The coverassembly of claim 45 wherein the plurality of spring extensionsdistribute the force uniformly on the heater backing plate.
 47. Thecover assembly of claim 45 wherein the spring retainer plate retains theat least one spring strip and allows the plurality of spring extensionsof the at least one spring strip to pass through the spring retainerplate.
 48. The cover assembly of claim 33 wherein the support plateretains a substantially planar shape under a loading force from theforce distribution system, while the loading force acts to deform theheater backing plate attached to the resistive heater.
 49. The coverassembly of claim 33 wherein the support plate has a plurality of ribslocated on a top surface of the support plate to provide stiffness tothe support plate while permitting the close travel of optical scanningequipment to pass between the plurality of ribs.
 50. The cover assemblyof claim 33 further comprising at least one heater slide to locate andguide the heater backing plate attached to the resistive heater in theflexible heating cover assembly.
 51. The cover assembly of claim 33wherein at least one heater slide controls a horizontal position of theheater backing plate attached to the resistive heater, while permittingsome freedom of movement in a vertical direction.
 52. The cover assemblyof claim 33 wherein the resistive heater, the heater backing plate, andthe support plate each comprise a plurality of aligned sample wellopenings, each sample well opening corresponding to a respective sampletube of the plurality of sample tubes.
 53. The cover assembly of claim33 further comprising an optical scanning equipment that collectsoptical data for quantitative PCR type experiments.
 54. The coverassembly of claim 33 wherein a plurality of mechanical interfacestransfer force between the flexible heating cover assembly and a thermalsystem base.
 55. The cover assembly of claim 33 wherein the flexibleheating cover assembly surrounds the top and extends over at least aportion of a side of a thermal system base.
 56. The cover assembly ofclaim 33 wherein the flexible heating cover assembly holds the pluralityof sample tubes in a plurality of sample wells of a thermal base systemby imparting a substantially uniform compressive force on the pluralityof sample tubes.
 57. The cover assembly of claim 33 wherein the flexibleheating cover assembly tends to thermally insulate the plurality ofsample tubes.
 58. The cover assembly of claim 33 wherein each sampletube extends for a substantial length in the flexible heating coverassembly.
 59. The cover assembly of claim 33 wherein the flexibleheating cover assembly is capable of withstanding thermally cycling ofthe samples of biological material.
 60. The cover assembly of claim 33wherein the flexible heating cover assembly helps to minimize theconvective heat loss to an ambient environment.
 61. A flexible heatingcover assembly for an apparatus for heating samples of biologicalmaterial with substantial temperature uniformity comprising: a housingincluding a plurality of end caps and a plurality of side bars allcomposed of a thermally insulating material; a resistive heater locatedwithin the housing, the resistive heater including at least one outerheater element area and at least one central heater element area toproduce a non-uniform heat distribution along a surface exposed to aplurality of sample tubes; a heater backing plate engaging the resistiveheater to provide protection and stability to the resistive heaterwherein the heater backing plate is thin and composed of a thermallyconductive material; at least one spring strip engaging a springretainer plate, wherein the least one spring strip has a plurality ofspring extensions to distribute a force uniformly over the heaterbacking plate; and a support plate providing sufficient stiffness toprovide a reaction force for the at least one spring strip engaging thespring retainer plate with minimal deflection of the support plate,wherein the resistive heater, the heater backing plate, the springretainer plate, and the support plate each comprise a plurality ofaligned sample well openings, each sample well opening corresponding toa respective sample tube of a plurality of sample tubes.
 62. Theflexible heating cover assembly of claim 61 wherein the resistive heateris thin to allow rapid heating and cooling during thermal cycling of theplurality of sample tubes.
 63. The flexible heating cover assembly ofclaim 61 wherein the at least one outer heater element area is C-shapedand located along an outer edge of a plurality of sample well openings.64. The flexible heating cover assembly of claim 61 wherein the at leastone outer heater element area includes a tapered section and curved endportions.
 65. The flexible heating cover assembly of claim 61 whereinthe resistive heater further comprises at least one heat carrier circuitthat is not electrically connected to a heater power source wherein theat least one heat carrier circuit transfers heater through the resistiveheater.
 66. The flexible heating cover assembly of claim 61 wherein theresistive heater further comprises a thermistor located toward a centerportion of the resistive heater to provide control of the vapor and thecondensation environment of the plurality of sample tubes.
 67. Theflexible heating cover assembly of claim 61 wherein the resistive heatercan move vertically within the flexible heating cover assembly toprovide a more uniform heat distribution.
 68. The flexible heating coverassembly of claim 61 wherein the heater backing plate further comprisesa plurality of narrow slots to promote the flexibility of the heaterbacking plate and minimize the retardation of heat transfer through theheater backing plate.
 69. The flexible heating cover assembly of claim61 wherein a top surface of the heater backing plate is treated tominimize reflecting or scattering of light from the top surface of theheater backing plate.
 70. The flexible heating cover assembly of claim61 wherein the spring retainer plate retains the at least one springstrip and allows the plurality of spring extensions of the at least onespring strip to pass through the spring retainer plate.
 71. The flexibleheating cover assembly of claim 61 wherein the support plate retains asubstantially planar shape under a loading force from the forcedistribution system, while the loading force acts to deform the heaterbacking plate attached to the resistive heater.
 72. The flexible heatingcover assembly of claim 61 wherein the support plate has a plurality ofribs located on a top surface of the support plate to provide stiffnessto the support plate while permitting the close travel of opticalscanning equipment to pass between the plurality of ribs.
 73. Theflexible heating cover assembly of claim 61 further comprising at leastone heater slide to locate and guide the heater backing plate attachedto the resistive heater in the flexible heating cover assembly.
 74. Theflexible heating cover assembly of claim 61 wherein at least one heaterslide controls a horizontal position of the heater backing plateattached to the resistive heater, while permitting some freedom ofmovement in a vertical direction.
 75. The flexible heating coverassembly of claim 61 further comprising an optical scanning equipmentthat collects optical data for quantitative PCR type experiments. 76.The flexible heating cover assembly of claim 61 wherein a plurality ofmechanical interfaces transfer force between the flexible heating coverassembly and a thermal system base.
 77. The flexible heating coverassembly of claim 61 wherein the flexible heating cover assemblysurrounds the top and extends over at least a portion of a side of athermal system base.
 78. The flexible heating cover assembly of claim 61wherein the flexible heating cover assembly holds the plurality ofsample tubes in a plurality of sample wells of a thermal system base byimparting a substantially uniform compressive force on the plurality ofsample tubes.
 79. The flexible heating cover assembly of claim 61wherein the flexible heating cover assembly tends to thermally insulatethe plurality of sample tubes.
 80. The flexible heating cover assemblyof claim 61 wherein each sample tube extends for a substantial length inthe flexible heating cover assembly.
 81. The flexible heating coverassembly of claim 61 wherein the flexible heating cover assembly iscapable of withstanding thermally cycling of the samples of biologicalmaterial.
 82. The flexible heating cover assembly of claim 61 whereinthe flexible heating cover assembly helps to minimize the convectiveheat loss to an ambient environment.